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Message-ID: <20091218011144.GA29573@redhat.com>
Date: Fri, 18 Dec 2009 02:11:44 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@...il.com>,
Andi Kleen <andi@...stfloor.org>,
Ananth Mavinakayanahalli <ananth@...ibm.com>,
Christoph Hellwig <hch@...radead.org>,
"Frank Ch. Eigler" <fche@...hat.com>, Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <peterz@...radead.org>,
Roland McGrath <roland@...hat.com>,
linux-kernel@...r.kernel.org, utrace-devel@...hat.com
Subject: [PATCH 7/7] utrace core
From: Roland McGrath <roland@...hat.com>
This adds the utrace facility, a new modular interface in the kernel
for implementing user thread tracing and debugging. This fits on top
of the tracehook_* layer, so the new code is well-isolated.
The new interface is in <linux/utrace.h> and the DocBook utrace book
describes it. It allows for multiple separate tracing engines to work
in parallel without interfering with each other. Higher-level tracing
facilities can be implemented as loadable kernel modules using this layer.
The new facility is made optional under CONFIG_UTRACE. It can only be
enabled on machines that have all the prerequisites and select
CONFIG_HAVE_ARCH_TRACEHOOK.
If CONFIG_UTRACE is set ptrace uses the utrace facilities, it can play
nicely with other utrace-based things tracing the same threads.
Signed-off-by: Roland McGrath <roland@...hat.com>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
Documentation/DocBook/Makefile | 2
Documentation/DocBook/utrace.tmpl | 590 +++++++++
fs/proc/array.c | 3
include/linux/sched.h | 5
include/linux/tracehook.h | 87 +
include/linux/utrace.h | 692 ++++++++++
init/Kconfig | 9
kernel/Makefile | 1
kernel/fork.c | 3
kernel/utrace.c | 2443 ++++++++++++++++++++++++++++++++++++++
10 files changed, 3833 insertions(+), 2 deletions(-)
--- V1/Documentation/DocBook/Makefile~7_UTRACE 2009-12-18 01:57:41.000000000 +0100
+++ V1/Documentation/DocBook/Makefile 2009-12-18 01:58:37.000000000 +0100
@@ -14,7 +14,7 @@ DOCBOOKS := z8530book.xml mcabook.xml de
genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \
mac80211.xml debugobjects.xml sh.xml regulator.xml \
alsa-driver-api.xml writing-an-alsa-driver.xml \
- tracepoint.xml media.xml
+ tracepoint.xml utrace.xml media.xml
###
# The build process is as follows (targets):
--- /dev/null 2009-12-15 18:13:27.615265787 +0100
+++ V1/Documentation/DocBook/utrace.tmpl 2009-12-18 01:58:37.000000000 +0100
@@ -0,0 +1,590 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="utrace">
+ <bookinfo>
+ <title>The utrace User Debugging Infrastructure</title>
+ </bookinfo>
+
+ <toc></toc>
+
+ <chapter id="concepts"><title>utrace concepts</title>
+
+ <sect1 id="intro"><title>Introduction</title>
+
+ <para>
+ <application>utrace</application> is infrastructure code for tracing
+ and controlling user threads. This is the foundation for writing
+ tracing engines, which can be loadable kernel modules.
+ </para>
+
+ <para>
+ The basic actors in <application>utrace</application> are the thread
+ and the tracing engine. A tracing engine is some body of code that
+ calls into the <filename><linux/utrace.h></filename>
+ interfaces, represented by a <structname>struct
+ utrace_engine_ops</structname>. (Usually it's a kernel module,
+ though the legacy <function>ptrace</function> support is a tracing
+ engine that is not in a kernel module.) The interface operates on
+ individual threads (<structname>struct task_struct</structname>).
+ If an engine wants to treat several threads as a group, that is up
+ to its higher-level code.
+ </para>
+
+ <para>
+ Tracing begins by attaching an engine to a thread, using
+ <function>utrace_attach_task</function> or
+ <function>utrace_attach_pid</function>. If successful, it returns a
+ pointer that is the handle used in all other calls.
+ </para>
+
+ </sect1>
+
+ <sect1 id="callbacks"><title>Events and Callbacks</title>
+
+ <para>
+ An attached engine does nothing by default. An engine makes something
+ happen by requesting callbacks via <function>utrace_set_events</function>
+ and poking the thread with <function>utrace_control</function>.
+ The synchronization issues related to these two calls
+ are discussed further below in <xref linkend="teardown"/>.
+ </para>
+
+ <para>
+ Events are specified using the macro
+ <constant>UTRACE_EVENT(<replaceable>type</replaceable>)</constant>.
+ Each event type is associated with a callback in <structname>struct
+ utrace_engine_ops</structname>. A tracing engine can leave unused
+ callbacks <constant>NULL</constant>. The only callbacks required
+ are those used by the event flags it sets.
+ </para>
+
+ <para>
+ Many engines can be attached to each thread. When a thread has an
+ event, each engine gets a callback if it has set the event flag for
+ that event type. For most events, engines are called in the order they
+ attached. Engines that attach after the event has occurred do not get
+ callbacks for that event. This includes any new engines just attached
+ by an existing engine's callback function. Once the sequence of
+ callbacks for that one event has completed, such new engines are then
+ eligible in the next sequence that starts when there is another event.
+ </para>
+
+ <para>
+ Event reporting callbacks have details particular to the event type,
+ but are all called in similar environments and have the same
+ constraints. Callbacks are made from safe points, where no locks
+ are held, no special resources are pinned (usually), and the
+ user-mode state of the thread is accessible. So, callback code has
+ a pretty free hand. But to be a good citizen, callback code should
+ never block for long periods. It is fine to block in
+ <function>kmalloc</function> and the like, but never wait for i/o or
+ for user mode to do something. If you need the thread to wait, use
+ <constant>UTRACE_STOP</constant> and return from the callback
+ quickly. When your i/o finishes or whatever, you can use
+ <function>utrace_control</function> to resume the thread.
+ </para>
+
+ <para>
+ The <constant>UTRACE_EVENT(SYSCALL_ENTRY)</constant> event is a special
+ case. While other events happen in the kernel when it will return to
+ user mode soon, this event happens when entering the kernel before it
+ will proceed with the work requested from user mode. Because of this
+ difference, the <function>report_syscall_entry</function> callback is
+ special in two ways. For this event, engines are called in reverse of
+ the normal order (this includes the <function>report_quiesce</function>
+ call that precedes a <function>report_syscall_entry</function> call).
+ This preserves the semantics that the last engine to attach is called
+ "closest to user mode"--the engine that is first to see a thread's user
+ state when it enters the kernel is also the last to see that state when
+ the thread returns to user mode. For the same reason, if these
+ callbacks use <constant>UTRACE_STOP</constant> (see the next section),
+ the thread stops immediately after callbacks rather than only when it's
+ ready to return to user mode; when allowed to resume, it will actually
+ attempt the system call indicated by the register values at that time.
+ </para>
+
+ </sect1>
+
+ <sect1 id="safely"><title>Stopping Safely</title>
+
+ <sect2 id="well-behaved"><title>Writing well-behaved callbacks</title>
+
+ <para>
+ Well-behaved callbacks are important to maintain two essential
+ properties of the interface. The first of these is that unrelated
+ tracing engines should not interfere with each other. If your engine's
+ event callback does not return quickly, then another engine won't get
+ the event notification in a timely manner. The second important
+ property is that tracing should be as noninvasive as possible to the
+ normal operation of the system overall and of the traced thread in
+ particular. That is, attached tracing engines should not perturb a
+ thread's behavior, except to the extent that changing its user-visible
+ state is explicitly what you want to do. (Obviously some perturbation
+ is unavoidable, primarily timing changes, ranging from small delays due
+ to the overhead of tracing, to arbitrary pauses in user code execution
+ when a user stops a thread with a debugger for examination.) Even when
+ you explicitly want the perturbation of making the traced thread block,
+ just blocking directly in your callback has more unwanted effects. For
+ example, the <constant>CLONE</constant> event callbacks are called when
+ the new child thread has been created but not yet started running; the
+ child can never be scheduled until the <constant>CLONE</constant>
+ tracing callbacks return. (This allows engines tracing the parent to
+ attach to the child.) If a <constant>CLONE</constant> event callback
+ blocks the parent thread, it also prevents the child thread from
+ running (even to process a <constant>SIGKILL</constant>). If what you
+ want is to make both the parent and child block, then use
+ <function>utrace_attach_task</function> on the child and then use
+ <constant>UTRACE_STOP</constant> on both threads. A more crucial
+ problem with blocking in callbacks is that it can prevent
+ <constant>SIGKILL</constant> from working. A thread that is blocking
+ due to <constant>UTRACE_STOP</constant> will still wake up and die
+ immediately when sent a <constant>SIGKILL</constant>, as all threads
+ should. Relying on the <application>utrace</application>
+ infrastructure rather than on private synchronization calls in event
+ callbacks is an important way to help keep tracing robustly
+ noninvasive.
+ </para>
+
+ </sect2>
+
+ <sect2 id="UTRACE_STOP"><title>Using <constant>UTRACE_STOP</constant></title>
+
+ <para>
+ To control another thread and access its state, it must be stopped
+ with <constant>UTRACE_STOP</constant>. This means that it is
+ stopped and won't start running again while we access it. When a
+ thread is not already stopped, <function>utrace_control</function>
+ returns <constant>-EINPROGRESS</constant> and an engine must wait
+ for an event callback when the thread is ready to stop. The thread
+ may be running on another CPU or may be blocked. When it is ready
+ to be examined, it will make callbacks to engines that set the
+ <constant>UTRACE_EVENT(QUIESCE)</constant> event bit. To wake up an
+ interruptible wait, use <constant>UTRACE_INTERRUPT</constant>.
+ </para>
+
+ <para>
+ As long as some engine has used <constant>UTRACE_STOP</constant> and
+ not called <function>utrace_control</function> to resume the thread,
+ then the thread will remain stopped. <constant>SIGKILL</constant>
+ will wake it up, but it will not run user code. When the stop is
+ cleared with <function>utrace_control</function> or a callback
+ return value, the thread starts running again.
+ (See also <xref linkend="teardown"/>.)
+ </para>
+
+ </sect2>
+
+ </sect1>
+
+ <sect1 id="teardown"><title>Tear-down Races</title>
+
+ <sect2 id="SIGKILL"><title>Primacy of <constant>SIGKILL</constant></title>
+ <para>
+ Ordinarily synchronization issues for tracing engines are kept fairly
+ straightforward by using <constant>UTRACE_STOP</constant>. You ask a
+ thread to stop, and then once it makes the
+ <function>report_quiesce</function> callback it cannot do anything else
+ that would result in another callback, until you let it with a
+ <function>utrace_control</function> call. This simple arrangement
+ avoids complex and error-prone code in each one of a tracing engine's
+ event callbacks to keep them serialized with the engine's other
+ operations done on that thread from another thread of control.
+ However, giving tracing engines complete power to keep a traced thread
+ stuck in place runs afoul of a more important kind of simplicity that
+ the kernel overall guarantees: nothing can prevent or delay
+ <constant>SIGKILL</constant> from making a thread die and release its
+ resources. To preserve this important property of
+ <constant>SIGKILL</constant>, it as a special case can break
+ <constant>UTRACE_STOP</constant> like nothing else normally can. This
+ includes both explicit <constant>SIGKILL</constant> signals and the
+ implicit <constant>SIGKILL</constant> sent to each other thread in the
+ same thread group by a thread doing an exec, or processing a fatal
+ signal, or making an <function>exit_group</function> system call. A
+ tracing engine can prevent a thread from beginning the exit or exec or
+ dying by signal (other than <constant>SIGKILL</constant>) if it is
+ attached to that thread, but once the operation begins, no tracing
+ engine can prevent or delay all other threads in the same thread group
+ dying.
+ </para>
+ </sect2>
+
+ <sect2 id="reap"><title>Final callbacks</title>
+ <para>
+ The <function>report_reap</function> callback is always the final event
+ in the life cycle of a traced thread. Tracing engines can use this as
+ the trigger to clean up their own data structures. The
+ <function>report_death</function> callback is always the penultimate
+ event a tracing engine might see; it's seen unless the thread was
+ already in the midst of dying when the engine attached. Many tracing
+ engines will have no interest in when a parent reaps a dead process,
+ and nothing they want to do with a zombie thread once it dies; for
+ them, the <function>report_death</function> callback is the natural
+ place to clean up data structures and detach. To facilitate writing
+ such engines robustly, given the asynchrony of
+ <constant>SIGKILL</constant>, and without error-prone manual
+ implementation of synchronization schemes, the
+ <application>utrace</application> infrastructure provides some special
+ guarantees about the <function>report_death</function> and
+ <function>report_reap</function> callbacks. It still takes some care
+ to be sure your tracing engine is robust to tear-down races, but these
+ rules make it reasonably straightforward and concise to handle a lot of
+ corner cases correctly.
+ </para>
+ </sect2>
+
+ <sect2 id="refcount"><title>Engine and task pointers</title>
+ <para>
+ The first sort of guarantee concerns the core data structures
+ themselves. <structname>struct utrace_engine</structname> is
+ a reference-counted data structure. While you hold a reference, an
+ engine pointer will always stay valid so that you can safely pass it to
+ any <application>utrace</application> call. Each call to
+ <function>utrace_attach_task</function> or
+ <function>utrace_attach_pid</function> returns an engine pointer with a
+ reference belonging to the caller. You own that reference until you
+ drop it using <function>utrace_engine_put</function>. There is an
+ implicit reference on the engine while it is attached. So if you drop
+ your only reference, and then use
+ <function>utrace_attach_task</function> without
+ <constant>UTRACE_ATTACH_CREATE</constant> to look up that same engine,
+ you will get the same pointer with a new reference to replace the one
+ you dropped, just like calling <function>utrace_engine_get</function>.
+ When an engine has been detached, either explicitly with
+ <constant>UTRACE_DETACH</constant> or implicitly after
+ <function>report_reap</function>, then any references you hold are all
+ that keep the old engine pointer alive.
+ </para>
+
+ <para>
+ There is nothing a kernel module can do to keep a <structname>struct
+ task_struct</structname> alive outside of
+ <function>rcu_read_lock</function>. When the task dies and is reaped
+ by its parent (or itself), that structure can be freed so that any
+ dangling pointers you have stored become invalid.
+ <application>utrace</application> will not prevent this, but it can
+ help you detect it safely. By definition, a task that has been reaped
+ has had all its engines detached. All
+ <application>utrace</application> calls can be safely called on a
+ detached engine if the caller holds a reference on that engine pointer,
+ even if the task pointer passed in the call is invalid. All calls
+ return <constant>-ESRCH</constant> for a detached engine, which tells
+ you that the task pointer you passed could be invalid now. Since
+ <function>utrace_control</function> and
+ <function>utrace_set_events</function> do not block, you can call those
+ inside a <function>rcu_read_lock</function> section and be sure after
+ they don't return <constant>-ESRCH</constant> that the task pointer is
+ still valid until <function>rcu_read_unlock</function>. The
+ infrastructure never holds task references of its own. Though neither
+ <function>rcu_read_lock</function> nor any other lock is held while
+ making a callback, it's always guaranteed that the <structname>struct
+ task_struct</structname> and the <structname>struct
+ utrace_engine</structname> passed as arguments remain valid
+ until the callback function returns.
+ </para>
+
+ <para>
+ The common means for safely holding task pointers that is available to
+ kernel modules is to use <structname>struct pid</structname>, which
+ permits <function>put_pid</function> from kernel modules. When using
+ that, the calls <function>utrace_attach_pid</function>,
+ <function>utrace_control_pid</function>,
+ <function>utrace_set_events_pid</function>, and
+ <function>utrace_barrier_pid</function> are available.
+ </para>
+ </sect2>
+
+ <sect2 id="reap-after-death">
+ <title>
+ Serialization of <constant>DEATH</constant> and <constant>REAP</constant>
+ </title>
+ <para>
+ The second guarantee is the serialization of
+ <constant>DEATH</constant> and <constant>REAP</constant> event
+ callbacks for a given thread. The actual reaping by the parent
+ (<function>release_task</function> call) can occur simultaneously
+ while the thread is still doing the final steps of dying, including
+ the <function>report_death</function> callback. If a tracing engine
+ has requested both <constant>DEATH</constant> and
+ <constant>REAP</constant> event reports, it's guaranteed that the
+ <function>report_reap</function> callback will not be made until
+ after the <function>report_death</function> callback has returned.
+ If the <function>report_death</function> callback itself detaches
+ from the thread, then the <function>report_reap</function> callback
+ will never be made. Thus it is safe for a
+ <function>report_death</function> callback to clean up data
+ structures and detach.
+ </para>
+ </sect2>
+
+ <sect2 id="interlock"><title>Interlock with final callbacks</title>
+ <para>
+ The final sort of guarantee is that a tracing engine will know for sure
+ whether or not the <function>report_death</function> and/or
+ <function>report_reap</function> callbacks will be made for a certain
+ thread. These tear-down races are disambiguated by the error return
+ values of <function>utrace_set_events</function> and
+ <function>utrace_control</function>. Normally
+ <function>utrace_control</function> called with
+ <constant>UTRACE_DETACH</constant> returns zero, and this means that no
+ more callbacks will be made. If the thread is in the midst of dying,
+ it returns <constant>-EALREADY</constant> to indicate that the
+ <constant>report_death</constant> callback may already be in progress;
+ when you get this error, you know that any cleanup your
+ <function>report_death</function> callback does is about to happen or
+ has just happened--note that if the <function>report_death</function>
+ callback does not detach, the engine remains attached until the thread
+ gets reaped. If the thread is in the midst of being reaped,
+ <function>utrace_control</function> returns <constant>-ESRCH</constant>
+ to indicate that the <function>report_reap</function> callback may
+ already be in progress; this means the engine is implicitly detached
+ when the callback completes. This makes it possible for a tracing
+ engine that has decided asynchronously to detach from a thread to
+ safely clean up its data structures, knowing that no
+ <function>report_death</function> or <function>report_reap</function>
+ callback will try to do the same. <constant>utrace_detach</constant>
+ returns <constant>-ESRCH</constant> when the <structname>struct
+ utrace_engine</structname> has already been detached, but is
+ still a valid pointer because of its reference count. A tracing engine
+ can use this to safely synchronize its own independent multiple threads
+ of control with each other and with its event callbacks that detach.
+ </para>
+
+ <para>
+ In the same vein, <function>utrace_set_events</function> normally
+ returns zero; if the target thread was stopped before the call, then
+ after a successful call, no event callbacks not requested in the new
+ flags will be made. It fails with <constant>-EALREADY</constant> if
+ you try to clear <constant>UTRACE_EVENT(DEATH)</constant> when the
+ <function>report_death</function> callback may already have begun, if
+ you try to clear <constant>UTRACE_EVENT(REAP)</constant> when the
+ <function>report_reap</function> callback may already have begun, or if
+ you try to newly set <constant>UTRACE_EVENT(DEATH)</constant> or
+ <constant>UTRACE_EVENT(QUIESCE)</constant> when the target is already
+ dead or dying. Like <function>utrace_control</function>, it returns
+ <constant>-ESRCH</constant> when the thread has already been detached
+ (including forcible detach on reaping). This lets the tracing engine
+ know for sure which event callbacks it will or won't see after
+ <function>utrace_set_events</function> has returned. By checking for
+ errors, it can know whether to clean up its data structures immediately
+ or to let its callbacks do the work.
+ </para>
+ </sect2>
+
+ <sect2 id="barrier"><title>Using <function>utrace_barrier</function></title>
+ <para>
+ When a thread is safely stopped, calling
+ <function>utrace_control</function> with <constant>UTRACE_DETACH</constant>
+ or calling <function>utrace_set_events</function> to disable some events
+ ensures synchronously that your engine won't get any more of the callbacks
+ that have been disabled (none at all when detaching). But these can also
+ be used while the thread is not stopped, when it might be simultaneously
+ making a callback to your engine. For this situation, these calls return
+ <constant>-EINPROGRESS</constant> when it's possible a callback is in
+ progress. If you are not prepared to have your old callbacks still run,
+ then you can synchronize to be sure all the old callbacks are finished,
+ using <function>utrace_barrier</function>. This is necessary if the
+ kernel module containing your callback code is going to be unloaded.
+ </para>
+ <para>
+ After using <constant>UTRACE_DETACH</constant> once, further calls to
+ <function>utrace_control</function> with the same engine pointer will
+ return <constant>-ESRCH</constant>. In contrast, after getting
+ <constant>-EINPROGRESS</constant> from
+ <function>utrace_set_events</function>, you can call
+ <function>utrace_set_events</function> again later and if it returns zero
+ then know the old callbacks have finished.
+ </para>
+ <para>
+ Unlike all other calls, <function>utrace_barrier</function> (and
+ <function>utrace_barrier_pid</function>) will accept any engine pointer you
+ hold a reference on, even if <constant>UTRACE_DETACH</constant> has already
+ been used. After any <function>utrace_control</function> or
+ <function>utrace_set_events</function> call (these do not block), you can
+ call <function>utrace_barrier</function> to block until callbacks have
+ finished. This returns <constant>-ESRCH</constant> only if the engine is
+ completely detached (finished all callbacks). Otherwise it waits
+ until the thread is definitely not in the midst of a callback to this
+ engine and then returns zero, but can return
+ <constant>-ERESTARTSYS</constant> if its wait is interrupted.
+ </para>
+ </sect2>
+
+</sect1>
+
+</chapter>
+
+<chapter id="core"><title>utrace core API</title>
+
+<para>
+ The utrace API is declared in <filename><linux/utrace.h></filename>.
+</para>
+
+!Iinclude/linux/utrace.h
+!Ekernel/utrace.c
+
+</chapter>
+
+<chapter id="machine"><title>Machine State</title>
+
+<para>
+ The <function>task_current_syscall</function> function can be used on any
+ valid <structname>struct task_struct</structname> at any time, and does
+ not even require that <function>utrace_attach_task</function> was used at all.
+</para>
+
+<para>
+ The other ways to access the registers and other machine-dependent state of
+ a task can only be used on a task that is at a known safe point. The safe
+ points are all the places where <function>utrace_set_events</function> can
+ request callbacks (except for the <constant>DEATH</constant> and
+ <constant>REAP</constant> events). So at any event callback, it is safe to
+ examine <varname>current</varname>.
+</para>
+
+<para>
+ One task can examine another only after a callback in the target task that
+ returns <constant>UTRACE_STOP</constant> so that task will not return to user
+ mode after the safe point. This guarantees that the task will not resume
+ until the same engine uses <function>utrace_control</function>, unless the
+ task dies suddenly. To examine safely, one must use a pair of calls to
+ <function>utrace_prepare_examine</function> and
+ <function>utrace_finish_examine</function> surrounding the calls to
+ <structname>struct user_regset</structname> functions or direct examination
+ of task data structures. <function>utrace_prepare_examine</function> returns
+ an error if the task is not properly stopped, or is dead. After a
+ successful examination, the paired <function>utrace_finish_examine</function>
+ call returns an error if the task ever woke up during the examination. If
+ so, any data gathered may be scrambled and should be discarded. This means
+ there was a spurious wake-up (which should not happen), or a sudden death.
+</para>
+
+<sect1 id="regset"><title><structname>struct user_regset</structname></title>
+
+<para>
+ The <structname>struct user_regset</structname> API
+ is declared in <filename><linux/regset.h></filename>.
+</para>
+
+!Finclude/linux/regset.h
+
+</sect1>
+
+<sect1 id="task_current_syscall">
+ <title><filename>System Call Information</filename></title>
+
+<para>
+ This function is declared in <filename><linux/ptrace.h></filename>.
+</para>
+
+!Elib/syscall.c
+
+</sect1>
+
+<sect1 id="syscall"><title><filename>System Call Tracing</filename></title>
+
+<para>
+ The arch API for system call information is declared in
+ <filename><asm/syscall.h></filename>.
+ Each of these calls can be used only at system call entry tracing,
+ or can be used only at system call exit and the subsequent safe points
+ before returning to user mode.
+ At system call entry tracing means either during a
+ <structfield>report_syscall_entry</structfield> callback,
+ or any time after that callback has returned <constant>UTRACE_STOP</constant>.
+</para>
+
+!Finclude/asm-generic/syscall.h
+
+</sect1>
+
+</chapter>
+
+<chapter id="internals"><title>Kernel Internals</title>
+
+<para>
+ This chapter covers the interface to the tracing infrastructure
+ from the core of the kernel and the architecture-specific code.
+ This is for maintainers of the kernel and arch code, and not relevant
+ to using the tracing facilities described in preceding chapters.
+</para>
+
+<sect1 id="tracehook"><title>Core Calls In</title>
+
+<para>
+ These calls are declared in <filename><linux/tracehook.h></filename>.
+ The core kernel calls these functions at various important places.
+</para>
+
+!Finclude/linux/tracehook.h
+
+</sect1>
+
+<sect1 id="arch"><title>Architecture Calls Out</title>
+
+<para>
+ An arch that has done all these things sets
+ <constant>CONFIG_HAVE_ARCH_TRACEHOOK</constant>.
+ This is required to enable the <application>utrace</application> code.
+</para>
+
+<sect2 id="arch-ptrace"><title><filename><asm/ptrace.h></filename></title>
+
+<para>
+ An arch defines these in <filename><asm/ptrace.h></filename>
+ if it supports hardware single-step or block-step features.
+</para>
+
+!Finclude/linux/ptrace.h arch_has_single_step arch_has_block_step
+!Finclude/linux/ptrace.h user_enable_single_step user_enable_block_step
+!Finclude/linux/ptrace.h user_disable_single_step
+
+</sect2>
+
+<sect2 id="arch-syscall">
+ <title><filename><asm/syscall.h></filename></title>
+
+ <para>
+ An arch provides <filename><asm/syscall.h></filename> that
+ defines these as inlines, or declares them as exported functions.
+ These interfaces are described in <xref linkend="syscall"/>.
+ </para>
+
+</sect2>
+
+<sect2 id="arch-tracehook">
+ <title><filename><linux/tracehook.h></filename></title>
+
+ <para>
+ An arch must define <constant>TIF_NOTIFY_RESUME</constant>
+ and <constant>TIF_SYSCALL_TRACE</constant>
+ in its <filename><asm/thread_info.h></filename>.
+ The arch code must call the following functions, all declared
+ in <filename><linux/tracehook.h></filename> and
+ described in <xref linkend="tracehook"/>:
+
+ <itemizedlist>
+ <listitem>
+ <para><function>tracehook_notify_resume</function></para>
+ </listitem>
+ <listitem>
+ <para><function>tracehook_report_syscall_entry</function></para>
+ </listitem>
+ <listitem>
+ <para><function>tracehook_report_syscall_exit</function></para>
+ </listitem>
+ <listitem>
+ <para><function>tracehook_signal_handler</function></para>
+ </listitem>
+ </itemizedlist>
+
+ </para>
+
+</sect2>
+
+</sect1>
+
+</chapter>
+
+</book>
--- V1/fs/proc/array.c~7_UTRACE 2009-12-18 01:57:41.000000000 +0100
+++ V1/fs/proc/array.c 2009-12-18 01:58:37.000000000 +0100
@@ -82,6 +82,7 @@
#include <linux/pid_namespace.h>
#include <linux/ptrace.h>
#include <linux/tracehook.h>
+#include <linux/utrace.h>
#include <linux/swapops.h>
#include <asm/pgtable.h>
@@ -189,6 +190,8 @@ static inline void task_state(struct seq
cred->uid, cred->euid, cred->suid, cred->fsuid,
cred->gid, cred->egid, cred->sgid, cred->fsgid);
+ task_utrace_proc_status(m, p);
+
task_lock(p);
if (p->files)
fdt = files_fdtable(p->files);
--- V1/include/linux/sched.h~7_UTRACE 2009-12-18 01:57:41.000000000 +0100
+++ V1/include/linux/sched.h 2009-12-18 01:58:37.000000000 +0100
@@ -1396,6 +1396,11 @@ struct task_struct {
#endif
seccomp_t seccomp;
+#ifdef CONFIG_UTRACE
+ struct utrace *utrace;
+ unsigned long utrace_flags;
+#endif
+
/* Thread group tracking */
u32 parent_exec_id;
u32 self_exec_id;
--- V1/include/linux/tracehook.h~7_UTRACE 2009-12-18 01:57:41.000000000 +0100
+++ V1/include/linux/tracehook.h 2009-12-18 01:58:37.000000000 +0100
@@ -49,6 +49,7 @@
#include <linux/sched.h>
#include <linux/ptrace.h>
#include <linux/security.h>
+#include <linux/utrace.h>
struct linux_binprm;
/**
@@ -63,6 +64,8 @@ struct linux_binprm;
*/
static inline int tracehook_expect_breakpoints(struct task_struct *task)
{
+ if (unlikely(task_utrace_flags(task) & UTRACE_EVENT(SIGNAL_CORE)))
+ return 1;
return (task_ptrace(task) & PT_PTRACED) != 0;
}
@@ -111,6 +114,9 @@ static inline void ptrace_report_syscall
static inline __must_check int tracehook_report_syscall_entry(
struct pt_regs *regs)
{
+ if ((task_utrace_flags(current) & UTRACE_EVENT(SYSCALL_ENTRY)) &&
+ utrace_report_syscall_entry(regs))
+ return 1;
ptrace_report_syscall(regs);
return 0;
}
@@ -134,6 +140,9 @@ static inline __must_check int tracehook
*/
static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
{
+ if (task_utrace_flags(current) & UTRACE_EVENT(SYSCALL_EXIT))
+ utrace_report_syscall_exit(regs);
+
if (step && (task_ptrace(current) & PT_PTRACED)) {
siginfo_t info;
user_single_step_siginfo(current, regs, &info);
@@ -201,6 +210,8 @@ static inline void tracehook_report_exec
struct linux_binprm *bprm,
struct pt_regs *regs)
{
+ if (unlikely(task_utrace_flags(current) & UTRACE_EVENT(EXEC)))
+ utrace_report_exec(fmt, bprm, regs);
if (!ptrace_event(PT_TRACE_EXEC, PTRACE_EVENT_EXEC, 0) &&
unlikely(task_ptrace(current) & PT_PTRACED))
send_sig(SIGTRAP, current, 0);
@@ -218,10 +229,37 @@ static inline void tracehook_report_exec
*/
static inline void tracehook_report_exit(long *exit_code)
{
+ if (unlikely(task_utrace_flags(current) & UTRACE_EVENT(EXIT)))
+ utrace_report_exit(exit_code);
ptrace_event(PT_TRACE_EXIT, PTRACE_EVENT_EXIT, *exit_code);
}
/**
+ * tracehook_init_task - task_struct has just been copied
+ * @task: new &struct task_struct just copied from parent
+ *
+ * Called from do_fork() when @task has just been duplicated.
+ * After this, @task will be passed to tracehook_free_task()
+ * even if the rest of its setup fails before it is fully created.
+ */
+static inline void tracehook_init_task(struct task_struct *task)
+{
+ utrace_init_task(task);
+}
+
+/**
+ * tracehook_free_task - task_struct is being freed
+ * @task: dead &struct task_struct being freed
+ *
+ * Called from free_task() when @task is no longer in use.
+ */
+static inline void tracehook_free_task(struct task_struct *task)
+{
+ if (task_utrace_struct(task))
+ utrace_free_task(task);
+}
+
+/**
* tracehook_prepare_clone - prepare for new child to be cloned
* @clone_flags: %CLONE_* flags from clone/fork/vfork system call
*
@@ -285,6 +323,8 @@ static inline void tracehook_report_clon
unsigned long clone_flags,
pid_t pid, struct task_struct *child)
{
+ if (unlikely(task_utrace_flags(current) & UTRACE_EVENT(CLONE)))
+ utrace_report_clone(clone_flags, child);
if (unlikely(task_ptrace(child))) {
/*
* It doesn't matter who attached/attaching to this
@@ -317,6 +357,9 @@ static inline void tracehook_report_clon
pid_t pid,
struct task_struct *child)
{
+ if (unlikely(task_utrace_flags(current) & UTRACE_EVENT(CLONE)) &&
+ (clone_flags & CLONE_VFORK))
+ utrace_finish_vfork(current);
if (unlikely(trace))
ptrace_event(0, trace, pid);
}
@@ -351,6 +394,10 @@ static inline void tracehook_report_vfor
*/
static inline void tracehook_prepare_release_task(struct task_struct *task)
{
+ /* see utrace_add_engine() about this barrier */
+ smp_mb();
+ if (task_utrace_flags(task))
+ utrace_maybe_reap(task, task_utrace_struct(task), true);
}
/**
@@ -365,6 +412,7 @@ static inline void tracehook_prepare_rel
static inline void tracehook_finish_release_task(struct task_struct *task)
{
ptrace_release_task(task);
+ BUG_ON(task->exit_state != EXIT_DEAD);
}
/**
@@ -386,6 +434,8 @@ static inline void tracehook_signal_hand
const struct k_sigaction *ka,
struct pt_regs *regs, int stepping)
{
+ if (task_utrace_flags(current))
+ utrace_signal_handler(current, stepping);
if (stepping && (task_ptrace(current) & PT_PTRACED))
ptrace_notify(SIGTRAP);
}
@@ -403,6 +453,8 @@ static inline void tracehook_signal_hand
static inline int tracehook_consider_ignored_signal(struct task_struct *task,
int sig)
{
+ if (unlikely(task_utrace_flags(task) & UTRACE_EVENT(SIGNAL_IGN)))
+ return 1;
return (task_ptrace(task) & PT_PTRACED) != 0;
}
@@ -422,6 +474,9 @@ static inline int tracehook_consider_ign
static inline int tracehook_consider_fatal_signal(struct task_struct *task,
int sig)
{
+ if (unlikely(task_utrace_flags(task) & (UTRACE_EVENT(SIGNAL_TERM) |
+ UTRACE_EVENT(SIGNAL_CORE))))
+ return 1;
return (task_ptrace(task) & PT_PTRACED) != 0;
}
@@ -436,6 +491,8 @@ static inline int tracehook_consider_fat
*/
static inline int tracehook_force_sigpending(void)
{
+ if (unlikely(task_utrace_flags(current)))
+ return utrace_interrupt_pending();
return 0;
}
@@ -465,6 +522,8 @@ static inline int tracehook_get_signal(s
siginfo_t *info,
struct k_sigaction *return_ka)
{
+ if (unlikely(task_utrace_flags(task)))
+ return utrace_get_signal(task, regs, info, return_ka);
return 0;
}
@@ -492,6 +551,8 @@ static inline int tracehook_get_signal(s
*/
static inline int tracehook_notify_jctl(int notify, int why)
{
+ if (task_utrace_flags(current) & UTRACE_EVENT(JCTL))
+ utrace_report_jctl(notify, why);
return notify ?: task_ptrace(current) ? why : 0;
}
@@ -502,6 +563,8 @@ static inline int tracehook_notify_jctl(
*/
static inline void tracehook_finish_jctl(void)
{
+ if (task_utrace_flags(current))
+ utrace_finish_stop();
}
#define DEATH_REAP -1
@@ -524,6 +587,8 @@ static inline void tracehook_finish_jctl
static inline int tracehook_notify_death(struct task_struct *task,
void **death_cookie, int group_dead)
{
+ *death_cookie = task_utrace_struct(task);
+
if (task_detached(task))
return task->ptrace ? SIGCHLD : DEATH_REAP;
@@ -560,6 +625,15 @@ static inline void tracehook_report_deat
int signal, void *death_cookie,
int group_dead)
{
+ /*
+ * If utrace_set_events() was just called to enable
+ * UTRACE_EVENT(DEATH), then we are obliged to call
+ * utrace_report_death() and not miss it. utrace_set_events()
+ * checks @task->exit_state under tasklist_lock to synchronize
+ * with exit_notify(), the caller.
+ */
+ if (task_utrace_flags(task) & _UTRACE_DEATH_EVENTS)
+ utrace_report_death(task, death_cookie, group_dead, signal);
}
#ifdef TIF_NOTIFY_RESUME
@@ -589,10 +663,21 @@ static inline void set_notify_resume(str
* asynchronously, this will be called again before we return to
* user mode.
*
- * Called without locks.
+ * Called without locks. However, on some machines this may be
+ * called with interrupts disabled.
*/
static inline void tracehook_notify_resume(struct pt_regs *regs)
{
+ struct task_struct *task = current;
+ /*
+ * Prevent the following store/load from getting ahead of the
+ * caller which clears TIF_NOTIFY_RESUME. This pairs with the
+ * implicit mb() before setting TIF_NOTIFY_RESUME in
+ * set_notify_resume().
+ */
+ smp_mb();
+ if (task_utrace_flags(task))
+ utrace_resume(task, regs);
}
#endif /* TIF_NOTIFY_RESUME */
--- /dev/null 2009-12-15 18:13:27.615265787 +0100
+++ V1/include/linux/utrace.h 2009-12-18 01:58:37.000000000 +0100
@@ -0,0 +1,692 @@
+/*
+ * utrace infrastructure interface for debugging user processes
+ *
+ * Copyright (C) 2006-2009 Red Hat, Inc. All rights reserved.
+ *
+ * This copyrighted material is made available to anyone wishing to use,
+ * modify, copy, or redistribute it subject to the terms and conditions
+ * of the GNU General Public License v.2.
+ *
+ * Red Hat Author: Roland McGrath.
+ *
+ * This interface allows for notification of interesting events in a
+ * thread. It also mediates access to thread state such as registers.
+ * Multiple unrelated users can be associated with a single thread.
+ * We call each of these a tracing engine.
+ *
+ * A tracing engine starts by calling utrace_attach_task() or
+ * utrace_attach_pid() on the chosen thread, passing in a set of hooks
+ * (&struct utrace_engine_ops), and some associated data. This produces a
+ * &struct utrace_engine, which is the handle used for all other
+ * operations. An attached engine has its ops vector, its data, and an
+ * event mask controlled by utrace_set_events().
+ *
+ * For each event bit that is set, that engine will get the
+ * appropriate ops->report_*() callback when the event occurs. The
+ * &struct utrace_engine_ops need not provide callbacks for an event
+ * unless the engine sets one of the associated event bits.
+ */
+
+#ifndef _LINUX_UTRACE_H
+#define _LINUX_UTRACE_H 1
+
+#include <linux/list.h>
+#include <linux/kref.h>
+#include <linux/signal.h>
+#include <linux/sched.h>
+
+struct linux_binprm;
+struct pt_regs;
+struct utrace;
+struct user_regset;
+struct user_regset_view;
+
+/*
+ * Event bits passed to utrace_set_events().
+ * These appear in &struct task_struct.@...ace_flags
+ * and &struct utrace_engine.@...gs.
+ */
+enum utrace_events {
+ _UTRACE_EVENT_QUIESCE, /* Thread is available for examination. */
+ _UTRACE_EVENT_REAP, /* Zombie reaped, no more tracing possible. */
+ _UTRACE_EVENT_CLONE, /* Successful clone/fork/vfork just done. */
+ _UTRACE_EVENT_EXEC, /* Successful execve just completed. */
+ _UTRACE_EVENT_EXIT, /* Thread exit in progress. */
+ _UTRACE_EVENT_DEATH, /* Thread has died. */
+ _UTRACE_EVENT_SYSCALL_ENTRY, /* User entered kernel for system call. */
+ _UTRACE_EVENT_SYSCALL_EXIT, /* Returning to user after system call. */
+ _UTRACE_EVENT_SIGNAL, /* Signal delivery will run a user handler. */
+ _UTRACE_EVENT_SIGNAL_IGN, /* No-op signal to be delivered. */
+ _UTRACE_EVENT_SIGNAL_STOP, /* Signal delivery will suspend. */
+ _UTRACE_EVENT_SIGNAL_TERM, /* Signal delivery will terminate. */
+ _UTRACE_EVENT_SIGNAL_CORE, /* Signal delivery will dump core. */
+ _UTRACE_EVENT_JCTL, /* Job control stop or continue completed. */
+ _UTRACE_NEVENTS
+};
+#define UTRACE_EVENT(type) (1UL << _UTRACE_EVENT_##type)
+
+/*
+ * All the kinds of signal events.
+ * These all use the @report_signal() callback.
+ */
+#define UTRACE_EVENT_SIGNAL_ALL (UTRACE_EVENT(SIGNAL) \
+ | UTRACE_EVENT(SIGNAL_IGN) \
+ | UTRACE_EVENT(SIGNAL_STOP) \
+ | UTRACE_EVENT(SIGNAL_TERM) \
+ | UTRACE_EVENT(SIGNAL_CORE))
+/*
+ * Both kinds of syscall events; these call the @report_syscall_entry()
+ * and @report_syscall_exit() callbacks, respectively.
+ */
+#define UTRACE_EVENT_SYSCALL \
+ (UTRACE_EVENT(SYSCALL_ENTRY) | UTRACE_EVENT(SYSCALL_EXIT))
+
+/*
+ * The event reports triggered synchronously by task death.
+ */
+#define _UTRACE_DEATH_EVENTS (UTRACE_EVENT(DEATH) | UTRACE_EVENT(QUIESCE))
+
+/*
+ * Hooks in <linux/tracehook.h> call these entry points to the utrace dispatch.
+ */
+void utrace_free_task(struct task_struct *);
+bool utrace_interrupt_pending(void);
+void utrace_resume(struct task_struct *, struct pt_regs *);
+void utrace_finish_stop(void);
+void utrace_maybe_reap(struct task_struct *, struct utrace *, bool);
+int utrace_get_signal(struct task_struct *, struct pt_regs *,
+ siginfo_t *, struct k_sigaction *);
+void utrace_report_clone(unsigned long, struct task_struct *);
+void utrace_finish_vfork(struct task_struct *);
+void utrace_report_exit(long *exit_code);
+void utrace_report_death(struct task_struct *, struct utrace *, bool, int);
+void utrace_report_jctl(int notify, int type);
+void utrace_report_exec(struct linux_binfmt *, struct linux_binprm *,
+ struct pt_regs *regs);
+bool utrace_report_syscall_entry(struct pt_regs *);
+void utrace_report_syscall_exit(struct pt_regs *);
+void utrace_signal_handler(struct task_struct *, int);
+
+#ifndef CONFIG_UTRACE
+
+/*
+ * <linux/tracehook.h> uses these accessors to avoid #ifdef CONFIG_UTRACE.
+ */
+static inline unsigned long task_utrace_flags(struct task_struct *task)
+{
+ return 0;
+}
+static inline struct utrace *task_utrace_struct(struct task_struct *task)
+{
+ return NULL;
+}
+static inline void utrace_init_task(struct task_struct *child)
+{
+}
+
+static inline void task_utrace_proc_status(struct seq_file *m,
+ struct task_struct *p)
+{
+}
+
+#else /* CONFIG_UTRACE */
+
+static inline unsigned long task_utrace_flags(struct task_struct *task)
+{
+ return task->utrace_flags;
+}
+
+static inline struct utrace *task_utrace_struct(struct task_struct *task)
+{
+ struct utrace *utrace;
+
+ /*
+ * This barrier ensures that any prior load of task->utrace_flags
+ * is ordered before this load of task->utrace. We use those
+ * utrace_flags checks in the hot path to decide to call into
+ * the utrace code. The first attach installs task->utrace before
+ * setting task->utrace_flags nonzero with implicit barrier in
+ * between, see utrace_add_engine().
+ */
+ smp_rmb();
+ utrace = task->utrace;
+
+ smp_read_barrier_depends(); /* See utrace_task_alloc(). */
+ return utrace;
+}
+
+static inline void utrace_init_task(struct task_struct *task)
+{
+ task->utrace_flags = 0;
+ task->utrace = NULL;
+}
+
+void task_utrace_proc_status(struct seq_file *m, struct task_struct *p);
+
+
+/*
+ * Version number of the API defined in this file. This will change
+ * whenever a tracing engine's code would need some updates to keep
+ * working. We maintain this here for the benefit of tracing engine code
+ * that is developed concurrently with utrace API improvements before they
+ * are merged into the kernel, making LINUX_VERSION_CODE checks unwieldy.
+ */
+#define UTRACE_API_VERSION 20091216
+
+/**
+ * enum utrace_resume_action - engine's choice of action for a traced task
+ * @UTRACE_STOP: Stay quiescent after callbacks.
+ * @UTRACE_INTERRUPT: Make @report_signal() callback soon.
+ * @UTRACE_REPORT: Make some callback soon.
+ * @UTRACE_SINGLESTEP: Resume in user mode for one instruction.
+ * @UTRACE_BLOCKSTEP: Resume in user mode until next branch.
+ * @UTRACE_RESUME: Resume normally in user mode.
+ * @UTRACE_DETACH: Detach my engine (implies %UTRACE_RESUME).
+ *
+ * See utrace_control() for detailed descriptions of each action. This is
+ * encoded in the @action argument and the return value for every callback
+ * with a &u32 return value.
+ *
+ * The order of these is important. When there is more than one engine,
+ * each supplies its choice and the smallest value prevails.
+ */
+enum utrace_resume_action {
+ UTRACE_STOP,
+ UTRACE_INTERRUPT,
+ UTRACE_REPORT,
+ UTRACE_SINGLESTEP,
+ UTRACE_BLOCKSTEP,
+ UTRACE_RESUME,
+ UTRACE_DETACH,
+ UTRACE_RESUME_MAX
+};
+#define UTRACE_RESUME_BITS (ilog2(UTRACE_RESUME_MAX) + 1)
+#define UTRACE_RESUME_MASK ((1 << UTRACE_RESUME_BITS) - 1)
+
+/**
+ * utrace_resume_action - &enum utrace_resume_action from callback action
+ * @action: &u32 callback @action argument or return value
+ *
+ * This extracts the &enum utrace_resume_action from @action,
+ * which is the @action argument to a &struct utrace_engine_ops
+ * callback or the return value from one.
+ */
+static inline enum utrace_resume_action utrace_resume_action(u32 action)
+{
+ return action & UTRACE_RESUME_MASK;
+}
+
+/**
+ * enum utrace_signal_action - disposition of signal
+ * @UTRACE_SIGNAL_DELIVER: Deliver according to sigaction.
+ * @UTRACE_SIGNAL_IGN: Ignore the signal.
+ * @UTRACE_SIGNAL_TERM: Terminate the process.
+ * @UTRACE_SIGNAL_CORE: Terminate with core dump.
+ * @UTRACE_SIGNAL_STOP: Deliver as absolute stop.
+ * @UTRACE_SIGNAL_TSTP: Deliver as job control stop.
+ * @UTRACE_SIGNAL_REPORT: Reporting before pending signals.
+ * @UTRACE_SIGNAL_HANDLER: Reporting after signal handler setup.
+ *
+ * This is encoded in the @action argument and the return value for
+ * a @report_signal() callback. It says what will happen to the
+ * signal described by the &siginfo_t parameter to the callback.
+ *
+ * The %UTRACE_SIGNAL_REPORT value is used in an @action argument when
+ * a tracing report is being made before dequeuing any pending signal.
+ * If this is immediately after a signal handler has been set up, then
+ * %UTRACE_SIGNAL_HANDLER is used instead. A @report_signal callback
+ * that uses %UTRACE_SIGNAL_DELIVER|%UTRACE_SINGLESTEP will ensure
+ * it sees a %UTRACE_SIGNAL_HANDLER report.
+ */
+enum utrace_signal_action {
+ UTRACE_SIGNAL_DELIVER = 0x00,
+ UTRACE_SIGNAL_IGN = 0x10,
+ UTRACE_SIGNAL_TERM = 0x20,
+ UTRACE_SIGNAL_CORE = 0x30,
+ UTRACE_SIGNAL_STOP = 0x40,
+ UTRACE_SIGNAL_TSTP = 0x50,
+ UTRACE_SIGNAL_REPORT = 0x60,
+ UTRACE_SIGNAL_HANDLER = 0x70
+};
+#define UTRACE_SIGNAL_MASK 0xf0
+#define UTRACE_SIGNAL_HOLD 0x100 /* Flag, push signal back on queue. */
+
+/**
+ * utrace_signal_action - &enum utrace_signal_action from callback action
+ * @action: @report_signal callback @action argument or return value
+ *
+ * This extracts the &enum utrace_signal_action from @action, which
+ * is the @action argument to a @report_signal callback or the
+ * return value from one.
+ */
+static inline enum utrace_signal_action utrace_signal_action(u32 action)
+{
+ return action & UTRACE_SIGNAL_MASK;
+}
+
+/**
+ * enum utrace_syscall_action - disposition of system call attempt
+ * @UTRACE_SYSCALL_RUN: Run the system call.
+ * @UTRACE_SYSCALL_ABORT: Don't run the system call.
+ *
+ * This is encoded in the @action argument and the return value for
+ * a @report_syscall_entry callback.
+ */
+enum utrace_syscall_action {
+ UTRACE_SYSCALL_RUN = 0x00,
+ UTRACE_SYSCALL_ABORT = 0x10
+};
+#define UTRACE_SYSCALL_MASK 0xf0
+#define UTRACE_SYSCALL_RESUMED 0x100 /* Flag, report_syscall_entry() repeats */
+
+/**
+ * utrace_syscall_action - &enum utrace_syscall_action from callback action
+ * @action: @report_syscall_entry callback @action or return value
+ *
+ * This extracts the &enum utrace_syscall_action from @action, which
+ * is the @action argument to a @report_syscall_entry callback or the
+ * return value from one.
+ */
+static inline enum utrace_syscall_action utrace_syscall_action(u32 action)
+{
+ return action & UTRACE_SYSCALL_MASK;
+}
+
+/*
+ * Flags for utrace_attach_task() and utrace_attach_pid().
+ */
+#define UTRACE_ATTACH_MATCH_OPS 0x0001 /* Match engines on ops. */
+#define UTRACE_ATTACH_MATCH_DATA 0x0002 /* Match engines on data. */
+#define UTRACE_ATTACH_MATCH_MASK 0x000f
+#define UTRACE_ATTACH_CREATE 0x0010 /* Attach a new engine. */
+#define UTRACE_ATTACH_EXCLUSIVE 0x0020 /* Refuse if existing match. */
+
+/**
+ * struct utrace_engine - per-engine structure
+ * @ops: &struct utrace_engine_ops pointer passed to utrace_attach_task()
+ * @data: engine-private &void * passed to utrace_attach_task()
+ * @flags: event mask set by utrace_set_events() plus internal flag bits
+ *
+ * The task itself never has to worry about engines detaching while
+ * it's doing event callbacks. These structures are removed from the
+ * task's active list only when it's stopped, or by the task itself.
+ *
+ * utrace_engine_get() and utrace_engine_put() maintain a reference count.
+ * When it drops to zero, the structure is freed. One reference is held
+ * implicitly while the engine is attached to its task.
+ */
+struct utrace_engine {
+/* private: */
+ struct kref kref;
+ void (*release)(void *);
+ struct list_head entry;
+
+/* public: */
+ const struct utrace_engine_ops *ops;
+ void *data;
+
+ unsigned long flags;
+};
+
+/**
+ * utrace_engine_get - acquire a reference on a &struct utrace_engine
+ * @engine: &struct utrace_engine pointer
+ *
+ * You must hold a reference on @engine, and you get another.
+ */
+static inline void utrace_engine_get(struct utrace_engine *engine)
+{
+ kref_get(&engine->kref);
+}
+
+void __utrace_engine_release(struct kref *);
+
+/**
+ * utrace_engine_put - release a reference on a &struct utrace_engine
+ * @engine: &struct utrace_engine pointer
+ *
+ * You must hold a reference on @engine, and you lose that reference.
+ * If it was the last one, @engine becomes an invalid pointer.
+ */
+static inline void utrace_engine_put(struct utrace_engine *engine)
+{
+ kref_put(&engine->kref, __utrace_engine_release);
+}
+
+/**
+ * struct utrace_engine_ops - tracing engine callbacks
+ *
+ * Each @report_*() callback corresponds to an %UTRACE_EVENT(*) bit.
+ * utrace_set_events() calls on @engine choose which callbacks will
+ * be made to @engine from @task.
+ *
+ * Most callbacks take an @action argument, giving the resume action
+ * chosen by other tracing engines. All callbacks take an @engine
+ * argument. The @report_reap callback takes a @task argument that
+ * might or might not be @current. All other @report_* callbacks
+ * report an event in the @current task.
+ *
+ * For some calls, @action also includes bits specific to that event
+ * and utrace_resume_action() is used to extract the resume action.
+ * This shows what would happen if @engine wasn't there, or will if
+ * the callback's return value uses %UTRACE_RESUME. This always
+ * starts as %UTRACE_RESUME when no other tracing is being done on
+ * this task.
+ *
+ * All return values contain &enum utrace_resume_action bits. For
+ * some calls, other bits specific to that kind of event are added to
+ * the resume action bits with OR. These are the same bits used in
+ * the @action argument. The resume action returned by a callback
+ * does not override previous engines' choices, it only says what
+ * @engine wants done. What @current actually does is the action that's
+ * most constrained among the choices made by all attached engines.
+ * See utrace_control() for more information on the actions.
+ *
+ * When %UTRACE_STOP is used in @report_syscall_entry, then @current
+ * stops before attempting the system call. In this case, another
+ * @report_syscall_entry callback will follow after @current resumes if
+ * %UTRACE_REPORT or %UTRACE_INTERRUPT was returned by some callback
+ * or passed to utrace_control(). In a second or later callback,
+ * %UTRACE_SYSCALL_RESUMED is set in the @action argument to indicate
+ * a repeat callback still waiting to attempt the same system call
+ * invocation. This repeat callback gives each engine an opportunity
+ * to reexamine registers another engine might have changed while
+ * @current was held in %UTRACE_STOP.
+ *
+ * In other cases, the resume action does not take effect until @current
+ * is ready to check for signals and return to user mode. If there
+ * are more callbacks to be made, the last round of calls determines
+ * the final action. A @report_quiesce callback with @event zero, or
+ * a @report_signal callback, will always be the last one made before
+ * @current resumes. Only %UTRACE_STOP is "sticky"--if @engine returned
+ * %UTRACE_STOP then @current stays stopped unless @engine returns
+ * different from a following callback.
+ *
+ * The report_death() and report_reap() callbacks do not take @action
+ * arguments, and only %UTRACE_DETACH is meaningful in the return value
+ * from a report_death() callback. None of the resume actions applies
+ * to a dead thread.
+ *
+ * All @report_*() hooks are called with no locks held, in a generally
+ * safe environment when we will be returning to user mode soon (or just
+ * entered the kernel). It is fine to block for memory allocation and
+ * the like, but all hooks are asynchronous and must not block on
+ * external events! If you want the thread to block, use %UTRACE_STOP
+ * in your hook's return value; then later wake it up with utrace_control().
+ *
+ * @report_quiesce:
+ * Requested by %UTRACE_EVENT(%QUIESCE).
+ * This does not indicate any event, but just that @current is in a
+ * safe place for examination. This call is made before each specific
+ * event callback, except for @report_reap. The @event argument gives
+ * the %UTRACE_EVENT(@which) value for the event occurring. This
+ * callback might be made for events @engine has not requested, if
+ * some other engine is tracing the event; calling utrace_set_events()
+ * call here can request the immediate callback for this occurrence of
+ * @event. @event is zero when there is no other event, @current is
+ * now ready to check for signals and return to user mode, and some
+ * engine has used %UTRACE_REPORT or %UTRACE_INTERRUPT to request this
+ * callback. For this case, if @report_signal is not %NULL, the
+ * @report_quiesce callback may be replaced with a @report_signal
+ * callback passing %UTRACE_SIGNAL_REPORT in its @action argument,
+ * whenever @current is entering the signal-check path anyway.
+ *
+ * @report_signal:
+ * Requested by %UTRACE_EVENT(%SIGNAL_*) or %UTRACE_EVENT(%QUIESCE).
+ * Use utrace_signal_action() and utrace_resume_action() on @action.
+ * The signal action is %UTRACE_SIGNAL_REPORT when some engine has
+ * used %UTRACE_REPORT or %UTRACE_INTERRUPT; the callback can choose
+ * to stop or to deliver an artificial signal, before pending signals.
+ * It's %UTRACE_SIGNAL_HANDLER instead when signal handler setup just
+ * finished (after a previous %UTRACE_SIGNAL_DELIVER return); this
+ * serves in lieu of any %UTRACE_SIGNAL_REPORT callback requested by
+ * %UTRACE_REPORT or %UTRACE_INTERRUPT, and is also implicitly
+ * requested by %UTRACE_SINGLESTEP or %UTRACE_BLOCKSTEP into the
+ * signal delivery. The other signal actions indicate a signal about
+ * to be delivered; the previous engine's return value sets the signal
+ * action seen by the the following engine's callback. The @info data
+ * can be changed at will, including @info->si_signo. The settings in
+ * @return_ka determines what %UTRACE_SIGNAL_DELIVER does. @orig_ka
+ * is what was in force before other tracing engines intervened, and
+ * it's %NULL when this report began as %UTRACE_SIGNAL_REPORT or
+ * %UTRACE_SIGNAL_HANDLER. For a report without a new signal, @info
+ * is left uninitialized and must be set completely by an engine that
+ * chooses to deliver a signal; if there was a previous @report_signal
+ * callback ending in %UTRACE_STOP and it was just resumed using
+ * %UTRACE_REPORT or %UTRACE_INTERRUPT, then @info is left unchanged
+ * from the previous callback. In this way, the original signal can
+ * be left in @info while returning %UTRACE_STOP|%UTRACE_SIGNAL_IGN
+ * and then found again when resuming with %UTRACE_INTERRUPT.
+ * The %UTRACE_SIGNAL_HOLD flag bit can be OR'd into the return value,
+ * and might be in @action if the previous engine returned it. This
+ * flag asks that the signal in @info be pushed back on @current's queue
+ * so that it will be seen again after whatever action is taken now.
+ *
+ * @report_clone:
+ * Requested by %UTRACE_EVENT(%CLONE).
+ * Event reported for parent, before the new task @child might run.
+ * @clone_flags gives the flags used in the clone system call, or
+ * equivalent flags for a fork() or vfork() system call. This
+ * function can use utrace_attach_task() on @child. Then passing
+ * %UTRACE_STOP to utrace_control() on @child here keeps the child
+ * stopped before it ever runs in user mode, %UTRACE_REPORT or
+ * %UTRACE_INTERRUPT ensures a callback from @child before it
+ * starts in user mode.
+ *
+ * @report_jctl:
+ * Requested by %UTRACE_EVENT(%JCTL).
+ * Job control event; @type is %CLD_STOPPED or %CLD_CONTINUED,
+ * indicating whether we are stopping or resuming now. If @notify
+ * is nonzero, @current is the last thread to stop and so will send
+ * %SIGCHLD to its parent after this callback; @notify reflects
+ * what the parent's %SIGCHLD has in @si_code, which can sometimes
+ * be %CLD_STOPPED even when @type is %CLD_CONTINUED.
+ *
+ * @report_exec:
+ * Requested by %UTRACE_EVENT(%EXEC).
+ * An execve system call has succeeded and the new program is about to
+ * start running. The initial user register state is handy to be tweaked
+ * directly in @regs. @fmt and @bprm gives the details of this exec.
+ *
+ * @report_syscall_entry:
+ * Requested by %UTRACE_EVENT(%SYSCALL_ENTRY).
+ * Thread has entered the kernel to request a system call.
+ * The user register state is handy to be tweaked directly in @regs.
+ * The @action argument contains an &enum utrace_syscall_action,
+ * use utrace_syscall_action() to extract it. The return value
+ * overrides the last engine's action for the system call.
+ * If the final action is %UTRACE_SYSCALL_ABORT, no system call
+ * is made. The details of the system call being attempted can
+ * be fetched here with syscall_get_nr() and syscall_get_arguments().
+ * The parameter registers can be changed with syscall_set_arguments().
+ * See above about the %UTRACE_SYSCALL_RESUMED flag in @action.
+ * Use %UTRACE_REPORT in the return value to guarantee you get
+ * another callback (with %UTRACE_SYSCALL_RESUMED flag) in case
+ * @current stops with %UTRACE_STOP before attempting the system call.
+ *
+ * @report_syscall_exit:
+ * Requested by %UTRACE_EVENT(%SYSCALL_EXIT).
+ * Thread is about to leave the kernel after a system call request.
+ * The user register state is handy to be tweaked directly in @regs.
+ * The results of the system call attempt can be examined here using
+ * syscall_get_error() and syscall_get_return_value(). It is safe
+ * here to call syscall_set_return_value() or syscall_rollback().
+ *
+ * @report_exit:
+ * Requested by %UTRACE_EVENT(%EXIT).
+ * Thread is exiting and cannot be prevented from doing so,
+ * but all its state is still live. The @code value will be
+ * the wait result seen by the parent, and can be changed by
+ * this engine or others. The @orig_code value is the real
+ * status, not changed by any tracing engine. Returning %UTRACE_STOP
+ * here keeps @current stopped before it cleans up its state and dies,
+ * so it can be examined by other processes. When @current is allowed
+ * to run, it will die and get to the @report_death callback.
+ *
+ * @report_death:
+ * Requested by %UTRACE_EVENT(%DEATH).
+ * Thread is really dead now. It might be reaped by its parent at
+ * any time, or self-reap immediately. Though the actual reaping
+ * may happen in parallel, a report_reap() callback will always be
+ * ordered after a report_death() callback.
+ *
+ * @report_reap:
+ * Requested by %UTRACE_EVENT(%REAP).
+ * Called when someone reaps the dead task (parent, init, or self).
+ * This means the parent called wait, or else this was a detached
+ * thread or a process whose parent ignores SIGCHLD.
+ * No more callbacks are made after this one.
+ * The engine is always detached.
+ * There is nothing more a tracing engine can do about this thread.
+ * After this callback, the @engine pointer will become invalid.
+ * The @task pointer may become invalid if get_task_struct() hasn't
+ * been used to keep it alive.
+ * An engine should always request this callback if it stores the
+ * @engine pointer or stores any pointer in @engine->data, so it
+ * can clean up its data structures.
+ * Unlike other callbacks, this can be called from the parent's context
+ * rather than from the traced thread itself--it must not delay the
+ * parent by blocking.
+ *
+ * @release:
+ * If not %NULL, this is called after the last utrace_engine_put()
+ * call for a &struct utrace_engine, which could be implicit after
+ * a %UTRACE_DETACH return from another callback. Its argument is
+ * the engine's @data member.
+ */
+struct utrace_engine_ops {
+ u32 (*report_quiesce)(u32 action, struct utrace_engine *engine,
+ unsigned long event);
+ u32 (*report_signal)(u32 action, struct utrace_engine *engine,
+ struct pt_regs *regs,
+ siginfo_t *info,
+ const struct k_sigaction *orig_ka,
+ struct k_sigaction *return_ka);
+ u32 (*report_clone)(u32 action, struct utrace_engine *engine,
+ unsigned long clone_flags,
+ struct task_struct *child);
+ u32 (*report_jctl)(u32 action, struct utrace_engine *engine,
+ int type, int notify);
+ u32 (*report_exec)(u32 action, struct utrace_engine *engine,
+ const struct linux_binfmt *fmt,
+ const struct linux_binprm *bprm,
+ struct pt_regs *regs);
+ u32 (*report_syscall_entry)(u32 action, struct utrace_engine *engine,
+ struct pt_regs *regs);
+ u32 (*report_syscall_exit)(u32 action, struct utrace_engine *engine,
+ struct pt_regs *regs);
+ u32 (*report_exit)(u32 action, struct utrace_engine *engine,
+ long orig_code, long *code);
+ u32 (*report_death)(struct utrace_engine *engine,
+ bool group_dead, int signal);
+ void (*report_reap)(struct utrace_engine *engine,
+ struct task_struct *task);
+ void (*release)(void *data);
+};
+
+/**
+ * struct utrace_examiner - private state for using utrace_prepare_examine()
+ *
+ * The members of &struct utrace_examiner are private to the implementation.
+ * This data type holds the state from a call to utrace_prepare_examine()
+ * to be used by a call to utrace_finish_examine().
+ */
+struct utrace_examiner {
+/* private: */
+ long state;
+ unsigned long ncsw;
+};
+
+/*
+ * These are the exported entry points for tracing engines to use.
+ * See kernel/utrace.c for their kerneldoc comments with interface details.
+ */
+struct utrace_engine *utrace_attach_task(struct task_struct *, int,
+ const struct utrace_engine_ops *,
+ void *);
+struct utrace_engine *utrace_attach_pid(struct pid *, int,
+ const struct utrace_engine_ops *,
+ void *);
+int __must_check utrace_control(struct task_struct *,
+ struct utrace_engine *,
+ enum utrace_resume_action);
+int __must_check utrace_set_events(struct task_struct *,
+ struct utrace_engine *,
+ unsigned long eventmask);
+int __must_check utrace_barrier(struct task_struct *,
+ struct utrace_engine *);
+int __must_check utrace_prepare_examine(struct task_struct *,
+ struct utrace_engine *,
+ struct utrace_examiner *);
+int __must_check utrace_finish_examine(struct task_struct *,
+ struct utrace_engine *,
+ struct utrace_examiner *);
+
+/**
+ * utrace_control_pid - control a thread being traced by a tracing engine
+ * @pid: thread to affect
+ * @engine: attached engine to affect
+ * @action: &enum utrace_resume_action for thread to do
+ *
+ * This is the same as utrace_control(), but takes a &struct pid
+ * pointer rather than a &struct task_struct pointer. The caller must
+ * hold a ref on @pid, but does not need to worry about the task
+ * staying valid. If it's been reaped so that @pid points nowhere,
+ * then this call returns -%ESRCH.
+ */
+static inline __must_check int utrace_control_pid(
+ struct pid *pid, struct utrace_engine *engine,
+ enum utrace_resume_action action)
+{
+ /*
+ * We don't bother with rcu_read_lock() here to protect the
+ * task_struct pointer, because utrace_control will return
+ * -ESRCH without looking at that pointer if the engine is
+ * already detached. A task_struct pointer can't die before
+ * all the engines are detached in release_task() first.
+ */
+ struct task_struct *task = pid_task(pid, PIDTYPE_PID);
+ return unlikely(!task) ? -ESRCH : utrace_control(task, engine, action);
+}
+
+/**
+ * utrace_set_events_pid - choose which event reports a tracing engine gets
+ * @pid: thread to affect
+ * @engine: attached engine to affect
+ * @eventmask: new event mask
+ *
+ * This is the same as utrace_set_events(), but takes a &struct pid
+ * pointer rather than a &struct task_struct pointer. The caller must
+ * hold a ref on @pid, but does not need to worry about the task
+ * staying valid. If it's been reaped so that @pid points nowhere,
+ * then this call returns -%ESRCH.
+ */
+static inline __must_check int utrace_set_events_pid(
+ struct pid *pid, struct utrace_engine *engine, unsigned long eventmask)
+{
+ struct task_struct *task = pid_task(pid, PIDTYPE_PID);
+ return unlikely(!task) ? -ESRCH :
+ utrace_set_events(task, engine, eventmask);
+}
+
+/**
+ * utrace_barrier_pid - synchronize with simultaneous tracing callbacks
+ * @pid: thread to affect
+ * @engine: engine to affect (can be detached)
+ *
+ * This is the same as utrace_barrier(), but takes a &struct pid
+ * pointer rather than a &struct task_struct pointer. The caller must
+ * hold a ref on @pid, but does not need to worry about the task
+ * staying valid. If it's been reaped so that @pid points nowhere,
+ * then this call returns -%ESRCH.
+ */
+static inline __must_check int utrace_barrier_pid(struct pid *pid,
+ struct utrace_engine *engine)
+{
+ struct task_struct *task = pid_task(pid, PIDTYPE_PID);
+ return unlikely(!task) ? -ESRCH : utrace_barrier(task, engine);
+}
+
+#endif /* CONFIG_UTRACE */
+
+#endif /* linux/utrace.h */
--- V1/init/Kconfig~7_UTRACE 2009-12-18 01:57:41.000000000 +0100
+++ V1/init/Kconfig 2009-12-18 01:58:37.000000000 +0100
@@ -310,6 +310,15 @@ config AUDIT_TREE
depends on AUDITSYSCALL
select INOTIFY
+config UTRACE
+ bool "Infrastructure for tracing and debugging user processes"
+ depends on EXPERIMENTAL
+ depends on HAVE_ARCH_TRACEHOOK
+ help
+ Enable the utrace process tracing interface. This is an internal
+ kernel interface exported to kernel modules, to track events in
+ user threads, extract and change user thread state.
+
menu "RCU Subsystem"
choice
--- V1/kernel/Makefile~7_UTRACE 2009-12-18 01:57:41.000000000 +0100
+++ V1/kernel/Makefile 2009-12-18 01:58:37.000000000 +0100
@@ -69,6 +69,7 @@ obj-$(CONFIG_IKCONFIG) += configs.o
obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o
obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
+obj-$(CONFIG_UTRACE) += utrace.o
obj-$(CONFIG_UTRACE) += ptrace-utrace.o
obj-$(CONFIG_AUDIT) += audit.o auditfilter.o audit_watch.o
obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
--- V1/kernel/fork.c~7_UTRACE 2009-12-18 01:57:41.000000000 +0100
+++ V1/kernel/fork.c 2009-12-18 01:58:37.000000000 +0100
@@ -153,6 +153,7 @@ void free_task(struct task_struct *tsk)
free_thread_info(tsk->stack);
rt_mutex_debug_task_free(tsk);
ftrace_graph_exit_task(tsk);
+ tracehook_free_task(tsk);
free_task_struct(tsk);
}
EXPORT_SYMBOL(free_task);
@@ -1023,6 +1024,8 @@ static struct task_struct *copy_process(
if (!p)
goto fork_out;
+ tracehook_init_task(p);
+
ftrace_graph_init_task(p);
rt_mutex_init_task(p);
--- /dev/null 2009-12-15 18:13:27.615265787 +0100
+++ V1/kernel/utrace.c 2009-12-18 01:58:37.000000000 +0100
@@ -0,0 +1,2443 @@
+/*
+ * utrace infrastructure interface for debugging user processes
+ *
+ * Copyright (C) 2006-2009 Red Hat, Inc. All rights reserved.
+ *
+ * This copyrighted material is made available to anyone wishing to use,
+ * modify, copy, or redistribute it subject to the terms and conditions
+ * of the GNU General Public License v.2.
+ *
+ * Red Hat Author: Roland McGrath.
+ */
+
+#include <linux/utrace.h>
+#include <linux/tracehook.h>
+#include <linux/regset.h>
+#include <asm/syscall.h>
+#include <linux/ptrace.h>
+#include <linux/err.h>
+#include <linux/sched.h>
+#include <linux/freezer.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/seq_file.h>
+
+
+/*
+ * Per-thread structure private to utrace implementation.
+ * If task_struct.utrace_flags is nonzero, task_struct.utrace
+ * has always been allocated first. Once allocated, it is
+ * never freed until free_task().
+ *
+ * The common event reporting loops are done by the task making the
+ * report without ever taking any locks. To facilitate this, the two
+ * lists @attached and @attaching work together for smooth asynchronous
+ * attaching with low overhead. Modifying either list requires @lock.
+ * The @attaching list can be modified any time while holding @lock.
+ * New engines being attached always go on this list.
+ *
+ * The @attached list is what the task itself uses for its reporting
+ * loops. When the task itself is not quiescent, it can use the
+ * @attached list without taking any lock. Nobody may modify the list
+ * when the task is not quiescent. When it is quiescent, that means
+ * that it won't run again without taking @lock itself before using
+ * the list.
+ *
+ * At each place where we know the task is quiescent (or it's current),
+ * while holding @lock, we call splice_attaching(), below. This moves
+ * the @attaching list members on to the end of the @attached list.
+ * Since this happens at the start of any reporting pass, any new
+ * engines attached asynchronously go on the stable @attached list
+ * in time to have their callbacks seen.
+ */
+struct utrace {
+ spinlock_t lock;
+ struct list_head attached, attaching;
+
+ struct task_struct *cloning;
+
+ struct utrace_engine *reporting;
+
+ enum utrace_resume_action resume:UTRACE_RESUME_BITS;
+ unsigned int signal_handler:1;
+ unsigned int vfork_stop:1; /* need utrace_stop() before vfork wait */
+ unsigned int death:1; /* in utrace_report_death() now */
+ unsigned int reap:1; /* release_task() has run */
+ unsigned int pending_attach:1; /* need splice_attaching() */
+};
+
+static struct kmem_cache *utrace_cachep;
+static struct kmem_cache *utrace_engine_cachep;
+static const struct utrace_engine_ops utrace_detached_ops; /* forward decl */
+
+static int __init utrace_init(void)
+{
+ utrace_cachep = KMEM_CACHE(utrace, SLAB_PANIC);
+ utrace_engine_cachep = KMEM_CACHE(utrace_engine, SLAB_PANIC);
+ return 0;
+}
+module_init(utrace_init);
+
+/*
+ * Set up @task.utrace for the first time. We can have races
+ * between two utrace_attach_task() calls here. The task_lock()
+ * governs installing the new pointer. If another one got in first,
+ * we just punt the new one we allocated.
+ *
+ * This returns false only in case of a memory allocation failure.
+ */
+static bool utrace_task_alloc(struct task_struct *task)
+{
+ struct utrace *utrace = kmem_cache_zalloc(utrace_cachep, GFP_KERNEL);
+ if (unlikely(!utrace))
+ return false;
+ spin_lock_init(&utrace->lock);
+ INIT_LIST_HEAD(&utrace->attached);
+ INIT_LIST_HEAD(&utrace->attaching);
+ utrace->resume = UTRACE_RESUME;
+ task_lock(task);
+ if (likely(!task->utrace)) {
+ /*
+ * This barrier makes sure the initialization of the struct
+ * precedes the installation of the pointer. This pairs
+ * with smp_read_barrier_depends() in task_utrace_struct().
+ */
+ smp_wmb();
+ task->utrace = utrace;
+ }
+ task_unlock(task);
+
+ if (unlikely(task->utrace != utrace))
+ kmem_cache_free(utrace_cachep, utrace);
+ return true;
+}
+
+/*
+ * This is called via tracehook_free_task() from free_task()
+ * when @task is being deallocated.
+ */
+void utrace_free_task(struct task_struct *task)
+{
+ kmem_cache_free(utrace_cachep, task->utrace);
+}
+
+/*
+ * This is calledwhen the task is safely quiescent, i.e. it won't consult
+ * utrace->attached without the lock. Move any engines attached
+ * asynchronously from @utrace->attaching onto the @utrace->attached list.
+ */
+static void splice_attaching(struct utrace *utrace)
+{
+ lockdep_assert_held(&utrace->lock);
+ list_splice_tail_init(&utrace->attaching, &utrace->attached);
+ utrace->pending_attach = 0;
+}
+
+/*
+ * This is the exported function used by the utrace_engine_put() inline.
+ */
+void __utrace_engine_release(struct kref *kref)
+{
+ struct utrace_engine *engine = container_of(kref, struct utrace_engine,
+ kref);
+ BUG_ON(!list_empty(&engine->entry));
+ if (engine->release)
+ (*engine->release)(engine->data);
+ kmem_cache_free(utrace_engine_cachep, engine);
+}
+EXPORT_SYMBOL_GPL(__utrace_engine_release);
+
+static bool engine_matches(struct utrace_engine *engine, int flags,
+ const struct utrace_engine_ops *ops, void *data)
+{
+ if ((flags & UTRACE_ATTACH_MATCH_OPS) && engine->ops != ops)
+ return false;
+ if ((flags & UTRACE_ATTACH_MATCH_DATA) && engine->data != data)
+ return false;
+ return engine->ops && engine->ops != &utrace_detached_ops;
+}
+
+static struct utrace_engine *find_matching_engine(
+ struct utrace *utrace, int flags,
+ const struct utrace_engine_ops *ops, void *data)
+{
+ struct utrace_engine *engine;
+ list_for_each_entry(engine, &utrace->attached, entry)
+ if (engine_matches(engine, flags, ops, data))
+ return engine;
+ list_for_each_entry(engine, &utrace->attaching, entry)
+ if (engine_matches(engine, flags, ops, data))
+ return engine;
+ return NULL;
+}
+
+/*
+ * Enqueue @engine, or maybe don't if UTRACE_ATTACH_EXCLUSIVE.
+ */
+static int utrace_add_engine(struct task_struct *target,
+ struct utrace *utrace,
+ struct utrace_engine *engine,
+ int flags,
+ const struct utrace_engine_ops *ops,
+ void *data)
+{
+ int ret;
+
+ spin_lock(&utrace->lock);
+
+ ret = -EEXIST;
+ if ((flags & UTRACE_ATTACH_EXCLUSIVE) &&
+ unlikely(find_matching_engine(utrace, flags, ops, data)))
+ goto unlock;
+
+ /*
+ * In case we had no engines before, make sure that
+ * utrace_flags is not zero. Since we did unlock+lock
+ * at least once after utrace_task_alloc() installed
+ * ->utrace, we have the necessary barrier which pairs
+ * with rmb() in task_utrace_struct().
+ */
+ ret = -ESRCH;
+ if (!target->utrace_flags) {
+ target->utrace_flags = UTRACE_EVENT(REAP);
+ /*
+ * If we race with tracehook_prepare_release_task()
+ * make sure that either it sees utrace_flags != 0
+ * or we see exit_state == EXIT_DEAD.
+ */
+ smp_mb();
+ if (unlikely(target->exit_state == EXIT_DEAD)) {
+ target->utrace_flags = 0;
+ goto unlock;
+ }
+ }
+
+ /*
+ * Put the new engine on the pending ->attaching list.
+ * Make sure it gets onto the ->attached list by the next
+ * time it's examined. Setting ->pending_attach ensures
+ * that start_report() takes the lock and splices the lists
+ * before the next new reporting pass.
+ *
+ * When target == current, it would be safe just to call
+ * splice_attaching() right here. But if we're inside a
+ * callback, that would mean the new engine also gets
+ * notified about the event that precipitated its own
+ * creation. This is not what the user wants.
+ */
+ list_add_tail(&engine->entry, &utrace->attaching);
+ utrace->pending_attach = 1;
+ ret = 0;
+unlock:
+ spin_unlock(&utrace->lock);
+
+ return ret;
+}
+
+/**
+ * utrace_attach_task - attach new engine, or look up an attached engine
+ * @target: thread to attach to
+ * @flags: flag bits combined with OR, see below
+ * @ops: callback table for new engine
+ * @data: engine private data pointer
+ *
+ * The caller must ensure that the @target thread does not get freed,
+ * i.e. hold a ref or be its parent. It is always safe to call this
+ * on @current, or on the @child pointer in a @report_clone callback.
+ * For most other cases, it's easier to use utrace_attach_pid() instead.
+ *
+ * UTRACE_ATTACH_CREATE:
+ * Create a new engine. If %UTRACE_ATTACH_CREATE is not specified, you
+ * only look up an existing engine already attached to the thread.
+ *
+ * UTRACE_ATTACH_EXCLUSIVE:
+ * Attempting to attach a second (matching) engine fails with -%EEXIST.
+ *
+ * UTRACE_ATTACH_MATCH_OPS: Only consider engines matching @ops.
+ * UTRACE_ATTACH_MATCH_DATA: Only consider engines matching @data.
+ *
+ * Calls with neither %UTRACE_ATTACH_MATCH_OPS nor %UTRACE_ATTACH_MATCH_DATA
+ * match the first among any engines attached to @target. That means that
+ * %UTRACE_ATTACH_EXCLUSIVE in such a call fails with -%EEXIST if there
+ * are any engines on @target at all.
+ */
+struct utrace_engine *utrace_attach_task(
+ struct task_struct *target, int flags,
+ const struct utrace_engine_ops *ops, void *data)
+{
+ struct utrace *utrace = task_utrace_struct(target);
+ struct utrace_engine *engine;
+ int ret;
+
+ if (!(flags & UTRACE_ATTACH_CREATE)) {
+ if (unlikely(!utrace))
+ return ERR_PTR(-ENOENT);
+ spin_lock(&utrace->lock);
+ engine = find_matching_engine(utrace, flags, ops, data);
+ if (engine)
+ utrace_engine_get(engine);
+ spin_unlock(&utrace->lock);
+ return engine ?: ERR_PTR(-ENOENT);
+ }
+
+ if (unlikely(!ops) || unlikely(ops == &utrace_detached_ops))
+ return ERR_PTR(-EINVAL);
+
+ if (unlikely(target->flags & PF_KTHREAD))
+ /*
+ * Silly kernel, utrace is for users!
+ */
+ return ERR_PTR(-EPERM);
+
+ if (!utrace) {
+ if (unlikely(!utrace_task_alloc(target)))
+ return ERR_PTR(-ENOMEM);
+ utrace = task_utrace_struct(target);
+ }
+
+ engine = kmem_cache_alloc(utrace_engine_cachep, GFP_KERNEL);
+ if (unlikely(!engine))
+ return ERR_PTR(-ENOMEM);
+
+ /*
+ * Initialize the new engine structure. It starts out with two
+ * refs: one ref to return, and one ref for being attached.
+ */
+ kref_set(&engine->kref, 2);
+ engine->flags = 0;
+ engine->ops = ops;
+ engine->data = data;
+ engine->release = ops->release;
+
+ ret = utrace_add_engine(target, utrace, engine, flags, ops, data);
+
+ if (unlikely(ret)) {
+ kmem_cache_free(utrace_engine_cachep, engine);
+ engine = ERR_PTR(ret);
+ }
+
+ return engine;
+}
+EXPORT_SYMBOL_GPL(utrace_attach_task);
+
+/**
+ * utrace_attach_pid - attach new engine, or look up an attached engine
+ * @pid: &struct pid pointer representing thread to attach to
+ * @flags: flag bits combined with OR, see utrace_attach_task()
+ * @ops: callback table for new engine
+ * @data: engine private data pointer
+ *
+ * This is the same as utrace_attach_task(), but takes a &struct pid
+ * pointer rather than a &struct task_struct pointer. The caller must
+ * hold a ref on @pid, but does not need to worry about the task
+ * staying valid. If it's been reaped so that @pid points nowhere,
+ * then this call returns -%ESRCH.
+ */
+struct utrace_engine *utrace_attach_pid(
+ struct pid *pid, int flags,
+ const struct utrace_engine_ops *ops, void *data)
+{
+ struct utrace_engine *engine = ERR_PTR(-ESRCH);
+ struct task_struct *task = get_pid_task(pid, PIDTYPE_PID);
+ if (task) {
+ engine = utrace_attach_task(task, flags, ops, data);
+ put_task_struct(task);
+ }
+ return engine;
+}
+EXPORT_SYMBOL_GPL(utrace_attach_pid);
+
+/*
+ * When an engine is detached, the target thread may still see it and
+ * make callbacks until it quiesces. We install a special ops vector
+ * with these two callbacks. When the target thread quiesces, it can
+ * safely free the engine itself. For any event we will always get
+ * the report_quiesce() callback first, so we only need this one
+ * pointer to be set. The only exception is report_reap(), so we
+ * supply that callback too.
+ */
+static u32 utrace_detached_quiesce(u32 action, struct utrace_engine *engine,
+ unsigned long event)
+{
+ return UTRACE_DETACH;
+}
+
+static void utrace_detached_reap(struct utrace_engine *engine,
+ struct task_struct *task)
+{
+}
+
+static const struct utrace_engine_ops utrace_detached_ops = {
+ .report_quiesce = &utrace_detached_quiesce,
+ .report_reap = &utrace_detached_reap
+};
+
+/*
+ * The caller has to hold a ref on the engine. If the attached flag is
+ * true (all but utrace_barrier() calls), the engine is supposed to be
+ * attached. If the attached flag is false (utrace_barrier() only),
+ * then return -ERESTARTSYS for an engine marked for detach but not yet
+ * fully detached. The task pointer can be invalid if the engine is
+ * detached.
+ *
+ * Get the utrace lock for the target task.
+ * Returns the struct if locked, or ERR_PTR(-errno).
+ *
+ * This has to be robust against races with:
+ * utrace_control(target, UTRACE_DETACH) calls
+ * UTRACE_DETACH after reports
+ * utrace_report_death
+ * utrace_release_task
+ */
+static struct utrace *get_utrace_lock(struct task_struct *target,
+ struct utrace_engine *engine,
+ bool attached)
+ __acquires(utrace->lock)
+{
+ struct utrace *utrace;
+
+ rcu_read_lock();
+
+ /*
+ * If this engine was already detached, bail out before we look at
+ * the task_struct pointer at all. If it's detached after this
+ * check, then RCU is still keeping this task_struct pointer valid.
+ *
+ * The ops pointer is NULL when the engine is fully detached.
+ * It's &utrace_detached_ops when it's marked detached but still
+ * on the list. In the latter case, utrace_barrier() still works,
+ * since the target might be in the middle of an old callback.
+ */
+ if (unlikely(!engine->ops)) {
+ rcu_read_unlock();
+ return ERR_PTR(-ESRCH);
+ }
+
+ if (unlikely(engine->ops == &utrace_detached_ops)) {
+ rcu_read_unlock();
+ return attached ? ERR_PTR(-ESRCH) : ERR_PTR(-ERESTARTSYS);
+ }
+
+ utrace = task_utrace_struct(target);
+ spin_lock(&utrace->lock);
+ if (unlikely(!engine->ops) ||
+ unlikely(engine->ops == &utrace_detached_ops)) {
+ /*
+ * By the time we got the utrace lock,
+ * it had been reaped or detached already.
+ */
+ spin_unlock(&utrace->lock);
+ utrace = ERR_PTR(-ESRCH);
+ if (!attached && engine->ops == &utrace_detached_ops)
+ utrace = ERR_PTR(-ERESTARTSYS);
+ }
+ rcu_read_unlock();
+
+ return utrace;
+}
+
+/*
+ * Now that we don't hold any locks, run through any
+ * detached engines and free their references. Each
+ * engine had one implicit ref while it was attached.
+ */
+static void put_detached_list(struct list_head *list)
+{
+ struct utrace_engine *engine, *next;
+ list_for_each_entry_safe(engine, next, list, entry) {
+ list_del_init(&engine->entry);
+ utrace_engine_put(engine);
+ }
+}
+
+/*
+ * We use an extra bit in utrace_engine.flags past the event bits,
+ * to record whether the engine is keeping the target thread stopped.
+ *
+ * This bit is set in task_struct.utrace_flags whenever it is set in any
+ * engine's flags. Only utrace_reset() resets it in utrace_flags.
+ */
+#define ENGINE_STOP (1UL << _UTRACE_NEVENTS)
+
+static void mark_engine_wants_stop(struct task_struct *task,
+ struct utrace_engine *engine)
+{
+ engine->flags |= ENGINE_STOP;
+ task->utrace_flags |= ENGINE_STOP;
+}
+
+static void clear_engine_wants_stop(struct utrace_engine *engine)
+{
+ engine->flags &= ~ENGINE_STOP;
+}
+
+static bool engine_wants_stop(struct utrace_engine *engine)
+{
+ return (engine->flags & ENGINE_STOP) != 0;
+}
+
+/**
+ * utrace_set_events - choose which event reports a tracing engine gets
+ * @target: thread to affect
+ * @engine: attached engine to affect
+ * @events: new event mask
+ *
+ * This changes the set of events for which @engine wants callbacks made.
+ *
+ * This fails with -%EALREADY and does nothing if you try to clear
+ * %UTRACE_EVENT(%DEATH) when the @report_death callback may already have
+ * begun, if you try to clear %UTRACE_EVENT(%REAP) when the @report_reap
+ * callback may already have begun, or if you try to newly set
+ * %UTRACE_EVENT(%DEATH) or %UTRACE_EVENT(%QUIESCE) when @target is
+ * already dead or dying.
+ *
+ * This can fail with -%ESRCH when @target has already been detached,
+ * including forcible detach on reaping.
+ *
+ * If @target was stopped before the call, then after a successful call,
+ * no event callbacks not requested in @events will be made; if
+ * %UTRACE_EVENT(%QUIESCE) is included in @events, then a
+ * @report_quiesce callback will be made when @target resumes.
+ *
+ * If @target was not stopped and @events excludes some bits that were
+ * set before, this can return -%EINPROGRESS to indicate that @target
+ * may have been making some callback to @engine. When this returns
+ * zero, you can be sure that no event callbacks you've disabled in
+ * @events can be made. If @events only sets new bits that were not set
+ * before on @engine, then -%EINPROGRESS will never be returned.
+ *
+ * To synchronize after an -%EINPROGRESS return, see utrace_barrier().
+ *
+ * When @target is @current, -%EINPROGRESS is not returned. But note
+ * that a newly-created engine will not receive any callbacks related to
+ * an event notification already in progress. This call enables @events
+ * callbacks to be made as soon as @engine becomes eligible for any
+ * callbacks, see utrace_attach_task().
+ *
+ * These rules provide for coherent synchronization based on %UTRACE_STOP,
+ * even when %SIGKILL is breaking its normal simple rules.
+ */
+int utrace_set_events(struct task_struct *target,
+ struct utrace_engine *engine,
+ unsigned long events)
+{
+ struct utrace *utrace;
+ unsigned long old_flags, old_utrace_flags;
+ int ret;
+
+ /*
+ * We just ignore the internal bit, so callers can use
+ * engine->flags to seed bitwise ops for our argument.
+ */
+ events &= ~ENGINE_STOP;
+
+ utrace = get_utrace_lock(target, engine, true);
+ if (unlikely(IS_ERR(utrace)))
+ return PTR_ERR(utrace);
+
+ old_utrace_flags = target->utrace_flags;
+ old_flags = engine->flags & ~ENGINE_STOP;
+
+ if (target->exit_state &&
+ (((events & ~old_flags) & _UTRACE_DEATH_EVENTS) ||
+ (utrace->death &&
+ ((old_flags & ~events) & _UTRACE_DEATH_EVENTS)) ||
+ (utrace->reap && ((old_flags & ~events) & UTRACE_EVENT(REAP))))) {
+ spin_unlock(&utrace->lock);
+ return -EALREADY;
+ }
+
+ /*
+ * When setting these flags, it's essential that we really
+ * synchronize with exit_notify(). They cannot be set after
+ * exit_notify() takes the tasklist_lock. By holding the read
+ * lock here while setting the flags, we ensure that the calls
+ * to tracehook_notify_death() and tracehook_report_death() will
+ * see the new flags. This ensures that utrace_release_task()
+ * knows positively that utrace_report_death() will be called or
+ * that it won't.
+ */
+ if ((events & ~old_utrace_flags) & _UTRACE_DEATH_EVENTS) {
+ read_lock(&tasklist_lock);
+ if (unlikely(target->exit_state)) {
+ read_unlock(&tasklist_lock);
+ spin_unlock(&utrace->lock);
+ return -EALREADY;
+ }
+ target->utrace_flags |= events;
+ read_unlock(&tasklist_lock);
+ }
+
+ engine->flags = events | (engine->flags & ENGINE_STOP);
+ target->utrace_flags |= events;
+
+ if ((events & UTRACE_EVENT_SYSCALL) &&
+ !(old_utrace_flags & UTRACE_EVENT_SYSCALL))
+ set_tsk_thread_flag(target, TIF_SYSCALL_TRACE);
+
+ ret = 0;
+ if ((old_flags & ~events) && target != current &&
+ !task_is_stopped_or_traced(target) && !target->exit_state) {
+ /*
+ * This barrier ensures that our engine->flags changes
+ * have hit before we examine utrace->reporting,
+ * pairing with the barrier in start_callback(). If
+ * @target has not yet hit finish_callback() to clear
+ * utrace->reporting, we might be in the middle of a
+ * callback to @engine.
+ */
+ smp_mb();
+ if (utrace->reporting == engine)
+ ret = -EINPROGRESS;
+ }
+
+ spin_unlock(&utrace->lock);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(utrace_set_events);
+
+/*
+ * Asynchronously mark an engine as being detached.
+ *
+ * This must work while the target thread races with us doing
+ * start_callback(), defined below. It uses smp_rmb() between checking
+ * @engine->flags and using @engine->ops. Here we change @engine->ops
+ * first, then use smp_wmb() before changing @engine->flags. This ensures
+ * it can check the old flags before using the old ops, or check the old
+ * flags before using the new ops, or check the new flags before using the
+ * new ops, but can never check the new flags before using the old ops.
+ * Hence, utrace_detached_ops might be used with any old flags in place.
+ * It has report_quiesce() and report_reap() callbacks to handle all cases.
+ */
+static void mark_engine_detached(struct utrace_engine *engine)
+{
+ engine->ops = &utrace_detached_ops;
+ smp_wmb();
+ engine->flags = UTRACE_EVENT(QUIESCE);
+}
+
+/*
+ * Get @target to stop and return true if it is already stopped now.
+ * If we return false, it will make some event callback soonish.
+ * Called with @utrace locked.
+ */
+static bool utrace_do_stop(struct task_struct *target, struct utrace *utrace)
+{
+ if (task_is_stopped(target)) {
+ /*
+ * Stopped is considered quiescent; when it wakes up, it will
+ * go through utrace_finish_stop() before doing anything else.
+ */
+ spin_lock_irq(&target->sighand->siglock);
+ if (likely(task_is_stopped(target)))
+ __set_task_state(target, TASK_TRACED);
+ spin_unlock_irq(&target->sighand->siglock);
+ } else if (utrace->resume > UTRACE_REPORT) {
+ utrace->resume = UTRACE_REPORT;
+ set_notify_resume(target);
+ }
+
+ return task_is_traced(target);
+}
+
+/*
+ * If the target is not dead it should not be in tracing
+ * stop any more. Wake it unless it's in job control stop.
+ */
+static void utrace_wakeup(struct task_struct *target, struct utrace *utrace)
+{
+ lockdep_assert_held(&utrace->lock);
+ spin_lock_irq(&target->sighand->siglock);
+ if (target->signal->flags & SIGNAL_STOP_STOPPED ||
+ target->signal->group_stop_count)
+ target->state = TASK_STOPPED;
+ else
+ wake_up_state(target, __TASK_TRACED);
+ spin_unlock_irq(&target->sighand->siglock);
+}
+
+/*
+ * This is called when there might be some detached engines on the list or
+ * some stale bits in @task->utrace_flags. Clean them up and recompute the
+ * flags. Returns true if we're now fully detached.
+ *
+ * Called with @utrace->lock held, returns with it released.
+ * After this returns, @utrace might be freed if everything detached.
+ */
+static bool utrace_reset(struct task_struct *task, struct utrace *utrace)
+ __releases(utrace->lock)
+{
+ struct utrace_engine *engine, *next;
+ unsigned long flags = 0;
+ LIST_HEAD(detached);
+
+ splice_attaching(utrace);
+
+ /*
+ * Update the set of events of interest from the union
+ * of the interests of the remaining tracing engines.
+ * For any engine marked detached, remove it from the list.
+ * We'll collect them on the detached list.
+ */
+ list_for_each_entry_safe(engine, next, &utrace->attached, entry) {
+ if (engine->ops == &utrace_detached_ops) {
+ engine->ops = NULL;
+ list_move(&engine->entry, &detached);
+ } else {
+ flags |= engine->flags | UTRACE_EVENT(REAP);
+ }
+ }
+
+ if (task->exit_state) {
+ /*
+ * Once it's already dead, we never install any flags
+ * except REAP. When ->exit_state is set and events
+ * like DEATH are not set, then they never can be set.
+ * This ensures that utrace_release_task() knows
+ * positively that utrace_report_death() can never run.
+ */
+ BUG_ON(utrace->death);
+ flags &= UTRACE_EVENT(REAP);
+ } else if (!(flags & UTRACE_EVENT_SYSCALL) &&
+ test_tsk_thread_flag(task, TIF_SYSCALL_TRACE)) {
+ clear_tsk_thread_flag(task, TIF_SYSCALL_TRACE);
+ }
+
+ if (!flags) {
+ /*
+ * No more engines, cleared out the utrace.
+ */
+ utrace->resume = UTRACE_RESUME;
+ utrace->signal_handler = 0;
+ }
+
+ /*
+ * If no more engines want it stopped, wake it up.
+ */
+ if (task_is_traced(task) && !(flags & ENGINE_STOP))
+ utrace_wakeup(task, utrace);
+
+ /*
+ * In theory spin_lock() doesn't imply rcu_read_lock().
+ * Once we clear ->utrace_flags this task_struct can go away
+ * because tracehook_prepare_release_task() path does not take
+ * utrace->lock when ->utrace_flags == 0.
+ */
+ rcu_read_lock();
+ task->utrace_flags = flags;
+ spin_unlock(&utrace->lock);
+ rcu_read_unlock();
+
+ put_detached_list(&detached);
+
+ return !flags;
+}
+
+void utrace_finish_stop(void)
+{
+ /*
+ * If we were task_is_traced() and then SIGKILL'ed, make
+ * sure we do nothing until the tracer drops utrace->lock.
+ */
+ if (unlikely(__fatal_signal_pending(current))) {
+ struct utrace *utrace = task_utrace_struct(current);
+ spin_unlock_wait(&utrace->lock);
+ }
+}
+
+/*
+ * Perform %UTRACE_STOP, i.e. block in TASK_TRACED until woken up.
+ * @task == current, @utrace == current->utrace, which is not locked.
+ * Return true if we were woken up by SIGKILL even though some utrace
+ * engine may still want us to stay stopped.
+ */
+static void utrace_stop(struct task_struct *task, struct utrace *utrace,
+ enum utrace_resume_action action)
+{
+relock:
+ spin_lock(&utrace->lock);
+
+ if (action < utrace->resume) {
+ /*
+ * Ensure a reporting pass when we're resumed.
+ */
+ utrace->resume = action;
+ if (action == UTRACE_INTERRUPT)
+ set_thread_flag(TIF_SIGPENDING);
+ else
+ set_thread_flag(TIF_NOTIFY_RESUME);
+ }
+
+ /*
+ * If the ENGINE_STOP bit is clear in utrace_flags, that means
+ * utrace_reset() ran after we processed some UTRACE_STOP return
+ * values from callbacks to get here. If all engines have detached
+ * or resumed us, we don't stop. This check doesn't require
+ * siglock, but it should follow the interrupt/report bookkeeping
+ * steps (this can matter for UTRACE_RESUME but not UTRACE_DETACH).
+ */
+ if (unlikely(!(task->utrace_flags & ENGINE_STOP))) {
+ utrace_reset(task, utrace);
+ if (task->utrace_flags & ENGINE_STOP)
+ goto relock;
+ return;
+ }
+
+ /*
+ * The siglock protects us against signals. As well as SIGKILL
+ * waking us up, we must synchronize with the signal bookkeeping
+ * for stop signals and SIGCONT.
+ */
+ spin_lock_irq(&task->sighand->siglock);
+
+ if (unlikely(__fatal_signal_pending(task))) {
+ spin_unlock_irq(&task->sighand->siglock);
+ spin_unlock(&utrace->lock);
+ return;
+ }
+
+ __set_current_state(TASK_TRACED);
+
+ /*
+ * If there is a group stop in progress,
+ * we must participate in the bookkeeping.
+ */
+ if (unlikely(task->signal->group_stop_count) &&
+ !--task->signal->group_stop_count)
+ task->signal->flags = SIGNAL_STOP_STOPPED;
+
+ spin_unlock_irq(&task->sighand->siglock);
+ spin_unlock(&utrace->lock);
+
+ /*
+ * If ptrace is among the reasons for this stop, do its
+ * notification now. This could not just be done in
+ * ptrace's own event report callbacks because it has to
+ * be done after we are in TASK_TRACED. This makes the
+ * synchronization with ptrace_do_wait() work right.
+ *
+ * It's only because of the bad old overloading of the do_wait()
+ * logic for handling ptrace stops that we need this special case
+ * here. One day we will clean up ptrace so it does not need to
+ * work this way. New things that are designed sensibly don't need
+ * a wakeup that synchronizes with tasklist_lock and ->state, so
+ * the proper utrace API does not try to support this weirdness.
+ */
+ ptrace_notify_stop(task);
+
+ schedule();
+
+ utrace_finish_stop();
+
+ /*
+ * While in TASK_TRACED, we were considered "frozen enough".
+ * Now that we woke up, it's crucial if we're supposed to be
+ * frozen that we freeze now before running anything substantial.
+ */
+ try_to_freeze();
+
+ /*
+ * While we were in TASK_TRACED, complete_signal() considered
+ * us "uninterested" in signal wakeups. Now make sure our
+ * TIF_SIGPENDING state is correct for normal running.
+ */
+ spin_lock_irq(&task->sighand->siglock);
+ recalc_sigpending();
+ spin_unlock_irq(&task->sighand->siglock);
+}
+
+/*
+ * Called by release_task() with @reap set to true.
+ * Called by utrace_report_death() with @reap set to false.
+ * On reap, make report_reap callbacks and clean out @utrace
+ * unless still making callbacks. On death, update bookkeeping
+ * and handle the reap work if release_task() came in first.
+ */
+void utrace_maybe_reap(struct task_struct *target, struct utrace *utrace,
+ bool reap)
+{
+ struct utrace_engine *engine, *next;
+
+ spin_lock(&utrace->lock);
+
+ if (reap) {
+ /*
+ * If the target will do some final callbacks but hasn't
+ * finished them yet, we know because it clears these event
+ * bits after it's done. Instead of cleaning up here and
+ * requiring utrace_report_death() to cope with it, we
+ * delay the REAP report and the teardown until after the
+ * target finishes its death reports.
+ */
+ utrace->reap = 1;
+
+ if (target->utrace_flags & _UTRACE_DEATH_EVENTS) {
+ spin_unlock(&utrace->lock);
+ return;
+ }
+ } else {
+ /*
+ * After we unlock with this flag clear, any competing
+ * utrace_control/utrace_set_events calls know that we've
+ * finished our callbacks and any detach bookkeeping.
+ */
+ utrace->death = 0;
+
+ if (!utrace->reap) {
+ /*
+ * We're just dead, not reaped yet. This will
+ * reset @target->utrace_flags so the later call
+ * with @reap set won't hit the check above.
+ */
+ utrace_reset(target, utrace);
+ return;
+ }
+ }
+
+ /*
+ * utrace_add_engine() checks ->utrace_flags != 0.
+ * Since @utrace->reap is set, nobody can set or clear
+ * UTRACE_EVENT(REAP) in @engine->flags or change
+ * @engine->ops, and nobody can change @utrace->attached.
+ */
+ target->utrace_flags = 0;
+ splice_attaching(utrace);
+ spin_unlock(&utrace->lock);
+
+ list_for_each_entry_safe(engine, next, &utrace->attached, entry) {
+ if (engine->flags & UTRACE_EVENT(REAP))
+ engine->ops->report_reap(engine, target);
+
+ engine->ops = NULL;
+ engine->flags = 0;
+ list_del_init(&engine->entry);
+
+ utrace_engine_put(engine);
+ }
+}
+
+/*
+ * You can't do anything to a dead task but detach it.
+ * If release_task() has been called, you can't do that.
+ *
+ * On the exit path, DEATH and QUIESCE event bits are set only
+ * before utrace_report_death() has taken the lock. At that point,
+ * the death report will come soon, so disallow detach until it's
+ * done. This prevents us from racing with it detaching itself.
+ *
+ * Called only when @target->exit_state is nonzero.
+ */
+static inline int utrace_control_dead(struct task_struct *target,
+ struct utrace *utrace,
+ enum utrace_resume_action action)
+{
+ lockdep_assert_held(&utrace->lock);
+
+ if (action != UTRACE_DETACH || unlikely(utrace->reap))
+ return -ESRCH;
+
+ if (unlikely(utrace->death))
+ /*
+ * We have already started the death report. We can't
+ * prevent the report_death and report_reap callbacks,
+ * so tell the caller they will happen.
+ */
+ return -EALREADY;
+
+ return 0;
+}
+
+/**
+ * utrace_control - control a thread being traced by a tracing engine
+ * @target: thread to affect
+ * @engine: attached engine to affect
+ * @action: &enum utrace_resume_action for thread to do
+ *
+ * This is how a tracing engine asks a traced thread to do something.
+ * This call is controlled by the @action argument, which has the
+ * same meaning as the &enum utrace_resume_action value returned by
+ * event reporting callbacks.
+ *
+ * If @target is already dead (@target->exit_state nonzero),
+ * all actions except %UTRACE_DETACH fail with -%ESRCH.
+ *
+ * The following sections describe each option for the @action argument.
+ *
+ * UTRACE_DETACH:
+ *
+ * After this, the @engine data structure is no longer accessible,
+ * and the thread might be reaped. The thread will start running
+ * again if it was stopped and no longer has any attached engines
+ * that want it stopped.
+ *
+ * If the @report_reap callback may already have begun, this fails
+ * with -%ESRCH. If the @report_death callback may already have
+ * begun, this fails with -%EALREADY.
+ *
+ * If @target is not already stopped, then a callback to this engine
+ * might be in progress or about to start on another CPU. If so,
+ * then this returns -%EINPROGRESS; the detach happens as soon as
+ * the pending callback is finished. To synchronize after an
+ * -%EINPROGRESS return, see utrace_barrier().
+ *
+ * If @target is properly stopped before utrace_control() is called,
+ * then after successful return it's guaranteed that no more callbacks
+ * to the @engine->ops vector will be made.
+ *
+ * The only exception is %SIGKILL (and exec or group-exit by another
+ * thread in the group), which can cause asynchronous @report_death
+ * and/or @report_reap callbacks even when %UTRACE_STOP was used.
+ * (In that event, this fails with -%ESRCH or -%EALREADY, see above.)
+ *
+ * UTRACE_STOP:
+ *
+ * This asks that @target stop running. This returns 0 only if
+ * @target is already stopped, either for tracing or for job
+ * control. Then @target will remain stopped until another
+ * utrace_control() call is made on @engine; @target can be woken
+ * only by %SIGKILL (or equivalent, such as exec or termination by
+ * another thread in the same thread group).
+ *
+ * This returns -%EINPROGRESS if @target is not already stopped.
+ * Then the effect is like %UTRACE_REPORT. A @report_quiesce or
+ * @report_signal callback will be made soon. Your callback can
+ * then return %UTRACE_STOP to keep @target stopped.
+ *
+ * This does not interrupt system calls in progress, including ones
+ * that sleep for a long time. For that, use %UTRACE_INTERRUPT.
+ * To interrupt system calls and then keep @target stopped, your
+ * @report_signal callback can return %UTRACE_STOP.
+ *
+ * UTRACE_RESUME:
+ *
+ * Just let @target continue running normally, reversing the effect
+ * of a previous %UTRACE_STOP. If another engine is keeping @target
+ * stopped, then it remains stopped until all engines let it resume.
+ * If @target was not stopped, this has no effect.
+ *
+ * UTRACE_REPORT:
+ *
+ * This is like %UTRACE_RESUME, but also ensures that there will be
+ * a @report_quiesce or @report_signal callback made soon. If
+ * @target had been stopped, then there will be a callback before it
+ * resumes running normally. If another engine is keeping @target
+ * stopped, then there might be no callbacks until all engines let
+ * it resume.
+ *
+ * Since this is meaningless unless @report_quiesce callbacks will
+ * be made, it returns -%EINVAL if @engine lacks %UTRACE_EVENT(%QUIESCE).
+ *
+ * UTRACE_INTERRUPT:
+ *
+ * This is like %UTRACE_REPORT, but ensures that @target will make a
+ * @report_signal callback before it resumes or delivers signals.
+ * If @target was in a system call or about to enter one, work in
+ * progress will be interrupted as if by %SIGSTOP. If another
+ * engine is keeping @target stopped, then there might be no
+ * callbacks until all engines let it resume.
+ *
+ * This gives @engine an opportunity to introduce a forced signal
+ * disposition via its @report_signal callback.
+ *
+ * UTRACE_SINGLESTEP:
+ *
+ * It's invalid to use this unless arch_has_single_step() returned true.
+ * This is like %UTRACE_RESUME, but resumes for one user instruction only.
+ *
+ * Note that passing %UTRACE_SINGLESTEP or %UTRACE_BLOCKSTEP to
+ * utrace_control() or returning it from an event callback alone does
+ * not necessarily ensure that stepping will be enabled. If there are
+ * more callbacks made to any engine before returning to user mode,
+ * then the resume action is chosen only by the last set of callbacks.
+ * To be sure, enable %UTRACE_EVENT(%QUIESCE) and look for the
+ * @report_quiesce callback with a zero event mask, or the
+ * @report_signal callback with %UTRACE_SIGNAL_REPORT.
+ *
+ * Since this is not robust unless @report_quiesce callbacks will
+ * be made, it returns -%EINVAL if @engine lacks %UTRACE_EVENT(%QUIESCE).
+ *
+ * UTRACE_BLOCKSTEP:
+ *
+ * It's invalid to use this unless arch_has_block_step() returned true.
+ * This is like %UTRACE_SINGLESTEP, but resumes for one whole basic
+ * block of user instructions.
+ *
+ * Since this is not robust unless @report_quiesce callbacks will
+ * be made, it returns -%EINVAL if @engine lacks %UTRACE_EVENT(%QUIESCE).
+ *
+ * %UTRACE_BLOCKSTEP devolves to %UTRACE_SINGLESTEP when another
+ * tracing engine is using %UTRACE_SINGLESTEP at the same time.
+ */
+int utrace_control(struct task_struct *target,
+ struct utrace_engine *engine,
+ enum utrace_resume_action action)
+{
+ struct utrace *utrace;
+ bool reset;
+ int ret;
+
+ if (unlikely(action >= UTRACE_RESUME_MAX)) {
+ WARN(1, "invalid action argument to utrace_control()!");
+ return -EINVAL;
+ }
+
+ /*
+ * This is a sanity check for a programming error in the caller.
+ * Their request can only work properly in all cases by relying on
+ * a follow-up callback, but they didn't set one up! This check
+ * doesn't do locking, but it shouldn't matter. The caller has to
+ * be synchronously sure the callback is set up to be operating the
+ * interface properly.
+ */
+ if (action >= UTRACE_REPORT && action < UTRACE_RESUME &&
+ unlikely(!(engine->flags & UTRACE_EVENT(QUIESCE)))) {
+ WARN(1, "utrace_control() with no QUIESCE callback in place!");
+ return -EINVAL;
+ }
+
+ utrace = get_utrace_lock(target, engine, true);
+ if (unlikely(IS_ERR(utrace)))
+ return PTR_ERR(utrace);
+
+ reset = task_is_traced(target);
+ ret = 0;
+
+ /*
+ * ->exit_state can change under us, this doesn't matter.
+ * We do not care about ->exit_state in fact, but we do
+ * care about ->reap and ->death. If either flag is set,
+ * we must also see ->exit_state != 0.
+ */
+ if (unlikely(target->exit_state)) {
+ ret = utrace_control_dead(target, utrace, action);
+ if (ret) {
+ spin_unlock(&utrace->lock);
+ return ret;
+ }
+ reset = true;
+ }
+
+ switch (action) {
+ case UTRACE_STOP:
+ mark_engine_wants_stop(target, engine);
+ if (!reset && !utrace_do_stop(target, utrace))
+ ret = -EINPROGRESS;
+ reset = false;
+ break;
+
+ case UTRACE_DETACH:
+ if (engine_wants_stop(engine))
+ target->utrace_flags &= ~ENGINE_STOP;
+ mark_engine_detached(engine);
+ reset = reset || utrace_do_stop(target, utrace);
+ if (!reset) {
+ /*
+ * As in utrace_set_events(), this barrier ensures
+ * that our engine->flags changes have hit before we
+ * examine utrace->reporting, pairing with the barrier
+ * in start_callback(). If @target has not yet hit
+ * finish_callback() to clear utrace->reporting, we
+ * might be in the middle of a callback to @engine.
+ */
+ smp_mb();
+ if (utrace->reporting == engine)
+ ret = -EINPROGRESS;
+ }
+ break;
+
+ case UTRACE_RESUME:
+ /*
+ * This and all other cases imply resuming if stopped.
+ * There might not be another report before it just
+ * resumes, so make sure single-step is not left set.
+ */
+ clear_engine_wants_stop(engine);
+ if (likely(reset))
+ user_disable_single_step(target);
+ break;
+
+ case UTRACE_BLOCKSTEP:
+ /*
+ * Resume from stopped, step one block.
+ * We fall through to treat it like UTRACE_SINGLESTEP.
+ */
+ if (unlikely(!arch_has_block_step())) {
+ WARN(1, "UTRACE_BLOCKSTEP when !arch_has_block_step()");
+ action = UTRACE_SINGLESTEP;
+ }
+
+ case UTRACE_SINGLESTEP:
+ /*
+ * Resume from stopped, step one instruction.
+ * We fall through to the UTRACE_REPORT case.
+ */
+ if (unlikely(!arch_has_single_step())) {
+ WARN(1,
+ "UTRACE_SINGLESTEP when !arch_has_single_step()");
+ reset = false;
+ ret = -EOPNOTSUPP;
+ break;
+ }
+
+ case UTRACE_REPORT:
+ /*
+ * Make the thread call tracehook_notify_resume() soon.
+ * But don't bother if it's already been interrupted.
+ * In that case, utrace_get_signal() will be reporting soon.
+ */
+ clear_engine_wants_stop(engine);
+ if (action < utrace->resume) {
+ utrace->resume = action;
+ set_notify_resume(target);
+ }
+ break;
+
+ case UTRACE_INTERRUPT:
+ /*
+ * Make the thread call tracehook_get_signal() soon.
+ */
+ clear_engine_wants_stop(engine);
+ if (utrace->resume == UTRACE_INTERRUPT)
+ break;
+ utrace->resume = UTRACE_INTERRUPT;
+
+ /*
+ * If it's not already stopped, interrupt it now. We need
+ * the siglock here in case it calls recalc_sigpending()
+ * and clears its own TIF_SIGPENDING. By taking the lock,
+ * we've serialized any later recalc_sigpending() after our
+ * setting of utrace->resume to force it on.
+ */
+ if (reset) {
+ /*
+ * This is really just to keep the invariant that
+ * TIF_SIGPENDING is set with UTRACE_INTERRUPT.
+ * When it's stopped, we know it's always going
+ * through utrace_get_signal() and will recalculate.
+ */
+ set_tsk_thread_flag(target, TIF_SIGPENDING);
+ } else {
+ struct sighand_struct *sighand;
+ unsigned long irqflags;
+ sighand = lock_task_sighand(target, &irqflags);
+ if (likely(sighand)) {
+ signal_wake_up(target, 0);
+ unlock_task_sighand(target, &irqflags);
+ }
+ }
+ break;
+
+ default:
+ BUG(); /* We checked it on entry. */
+ }
+
+ /*
+ * Let the thread resume running. If it's not stopped now,
+ * there is nothing more we need to do.
+ */
+ if (reset)
+ utrace_reset(target, utrace);
+ else
+ spin_unlock(&utrace->lock);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(utrace_control);
+
+/**
+ * utrace_barrier - synchronize with simultaneous tracing callbacks
+ * @target: thread to affect
+ * @engine: engine to affect (can be detached)
+ *
+ * This blocks while @target might be in the midst of making a callback to
+ * @engine. It can be interrupted by signals and will return -%ERESTARTSYS.
+ * A return value of zero means no callback from @target to @engine was
+ * in progress. Any effect of its return value (such as %UTRACE_STOP) has
+ * already been applied to @engine.
+ *
+ * It's not necessary to keep the @target pointer alive for this call.
+ * It's only necessary to hold a ref on @engine. This will return
+ * safely even if @target has been reaped and has no task refs.
+ *
+ * A successful return from utrace_barrier() guarantees its ordering
+ * with respect to utrace_set_events() and utrace_control() calls. If
+ * @target was not properly stopped, event callbacks just disabled might
+ * still be in progress; utrace_barrier() waits until there is no chance
+ * an unwanted callback can be in progress.
+ */
+int utrace_barrier(struct task_struct *target, struct utrace_engine *engine)
+{
+ struct utrace *utrace;
+ int ret = -ERESTARTSYS;
+
+ if (unlikely(target == current))
+ return 0;
+
+ do {
+ utrace = get_utrace_lock(target, engine, false);
+ if (unlikely(IS_ERR(utrace))) {
+ ret = PTR_ERR(utrace);
+ if (ret != -ERESTARTSYS)
+ break;
+ } else {
+ /*
+ * All engine state changes are done while
+ * holding the lock, i.e. before we get here.
+ * Since we have the lock, we only need to
+ * worry about @target making a callback.
+ * When it has entered start_callback() but
+ * not yet gotten to finish_callback(), we
+ * will see utrace->reporting == @engine.
+ * When @target doesn't take the lock, it uses
+ * barriers to order setting utrace->reporting
+ * before it examines the engine state.
+ */
+ if (utrace->reporting != engine)
+ ret = 0;
+ spin_unlock(&utrace->lock);
+ if (!ret)
+ break;
+ }
+ schedule_timeout_interruptible(1);
+ } while (!signal_pending(current));
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(utrace_barrier);
+
+/*
+ * This is local state used for reporting loops, perhaps optimized away.
+ */
+struct utrace_report {
+ u32 result;
+ enum utrace_resume_action action;
+ enum utrace_resume_action resume_action;
+ bool detaches;
+ bool spurious;
+};
+
+#define INIT_REPORT(var) \
+ struct utrace_report var = { \
+ .action = UTRACE_RESUME, \
+ .resume_action = UTRACE_RESUME, \
+ .spurious = true \
+ }
+
+/*
+ * We are now making the report, so clear the flag saying we need one.
+ * When there is a new attach, ->pending_attach is set just so we will
+ * know to do splice_attaching() here before the callback loop.
+ */
+static enum utrace_resume_action start_report(struct utrace *utrace)
+{
+ enum utrace_resume_action resume = utrace->resume;
+ if (utrace->pending_attach ||
+ (resume > UTRACE_INTERRUPT && resume < UTRACE_RESUME)) {
+ spin_lock(&utrace->lock);
+ splice_attaching(utrace);
+ resume = utrace->resume;
+ if (resume > UTRACE_INTERRUPT)
+ utrace->resume = UTRACE_RESUME;
+ spin_unlock(&utrace->lock);
+ }
+ return resume;
+}
+
+static inline void finish_report_reset(struct task_struct *task,
+ struct utrace *utrace,
+ struct utrace_report *report)
+{
+ if (unlikely(report->spurious || report->detaches)) {
+ spin_lock(&utrace->lock);
+ if (utrace_reset(task, utrace))
+ report->action = UTRACE_RESUME;
+ }
+}
+
+/*
+ * Complete a normal reporting pass, pairing with a start_report() call.
+ * This handles any UTRACE_DETACH or UTRACE_REPORT or UTRACE_INTERRUPT
+ * returns from engine callbacks. If @will_not_stop is true and any
+ * engine's last callback used UTRACE_STOP, we do UTRACE_REPORT here to
+ * ensure we stop before user mode. If there were no callbacks made, it
+ * will recompute @task->utrace_flags to avoid another false-positive.
+ */
+static void finish_report(struct task_struct *task, struct utrace *utrace,
+ struct utrace_report *report, bool will_not_stop)
+{
+ enum utrace_resume_action resume = report->action;
+
+ if (resume == UTRACE_STOP)
+ resume = will_not_stop ? UTRACE_REPORT : UTRACE_RESUME;
+
+ if (resume < utrace->resume) {
+ spin_lock(&utrace->lock);
+ utrace->resume = resume;
+ if (resume == UTRACE_INTERRUPT)
+ set_tsk_thread_flag(task, TIF_SIGPENDING);
+ else
+ set_tsk_thread_flag(task, TIF_NOTIFY_RESUME);
+ spin_unlock(&utrace->lock);
+ }
+
+ finish_report_reset(task, utrace, report);
+}
+
+static void finish_callback_report(struct task_struct *task,
+ struct utrace *utrace,
+ struct utrace_report *report,
+ struct utrace_engine *engine,
+ enum utrace_resume_action action)
+{
+ if (action == UTRACE_DETACH) {
+ /*
+ * By holding the lock here, we make sure that
+ * utrace_barrier() (really get_utrace_lock()) sees the
+ * effect of this detach. Otherwise utrace_barrier() could
+ * return 0 after this callback had returned UTRACE_DETACH.
+ * This way, a 0 return is an unambiguous indicator that any
+ * callback returning UTRACE_DETACH has indeed caused detach.
+ */
+ spin_lock(&utrace->lock);
+ engine->ops = &utrace_detached_ops;
+ spin_unlock(&utrace->lock);
+ }
+
+ /*
+ * If utrace_control() was used, treat that like UTRACE_DETACH here.
+ */
+ if (engine->ops == &utrace_detached_ops) {
+ report->detaches = true;
+ return;
+ }
+
+ if (action < report->action)
+ report->action = action;
+
+ if (action != UTRACE_STOP) {
+ if (action < report->resume_action)
+ report->resume_action = action;
+
+ if (engine_wants_stop(engine)) {
+ spin_lock(&utrace->lock);
+ clear_engine_wants_stop(engine);
+ spin_unlock(&utrace->lock);
+ }
+
+ return;
+ }
+
+ if (!engine_wants_stop(engine)) {
+ spin_lock(&utrace->lock);
+ /*
+ * If utrace_control() came in and detached us
+ * before we got the lock, we must not stop now.
+ */
+ if (unlikely(engine->ops == &utrace_detached_ops))
+ report->detaches = true;
+ else
+ mark_engine_wants_stop(task, engine);
+ spin_unlock(&utrace->lock);
+ }
+}
+
+/*
+ * Apply the return value of one engine callback to @report.
+ * Returns true if @engine detached and should not get any more callbacks.
+ */
+static bool finish_callback(struct task_struct *task, struct utrace *utrace,
+ struct utrace_report *report,
+ struct utrace_engine *engine,
+ u32 ret)
+{
+ report->result = ret & ~UTRACE_RESUME_MASK;
+ finish_callback_report(task, utrace, report, engine,
+ utrace_resume_action(ret));
+
+ /*
+ * Now that we have applied the effect of the return value,
+ * clear this so that utrace_barrier() can stop waiting.
+ * A subsequent utrace_control() can stop or resume @engine
+ * and know this was ordered after its callback's action.
+ *
+ * We don't need any barriers here because utrace_barrier()
+ * takes utrace->lock. If we touched engine->flags above,
+ * the lock guaranteed this change was before utrace_barrier()
+ * examined utrace->reporting.
+ */
+ utrace->reporting = NULL;
+
+ /*
+ * We've just done an engine callback. These are allowed to sleep,
+ * though all well-behaved ones restrict that to blocking kalloc()
+ * or quickly-acquired mutex_lock() and the like. This is a good
+ * place to make sure tracing engines don't introduce too much
+ * latency under voluntary preemption.
+ */
+ might_sleep();
+
+ return engine->ops == &utrace_detached_ops;
+}
+
+/*
+ * Start the callbacks for @engine to consider @event (a bit mask).
+ * This makes the report_quiesce() callback first. If @engine wants
+ * a specific callback for @event, we return the ops vector to use.
+ * If not, we return NULL. The return value from the ops->callback
+ * function called should be passed to finish_callback().
+ */
+static const struct utrace_engine_ops *start_callback(
+ struct utrace *utrace, struct utrace_report *report,
+ struct utrace_engine *engine, struct task_struct *task,
+ unsigned long event)
+{
+ const struct utrace_engine_ops *ops;
+ unsigned long want;
+
+ /*
+ * This barrier ensures that we've set utrace->reporting before
+ * we examine engine->flags or engine->ops. utrace_barrier()
+ * relies on this ordering to indicate that the effect of any
+ * utrace_control() and utrace_set_events() calls is in place
+ * by the time utrace->reporting can be seen to be NULL.
+ */
+ utrace->reporting = engine;
+ smp_mb();
+
+ /*
+ * This pairs with the barrier in mark_engine_detached().
+ * It makes sure that we never see the old ops vector with
+ * the new flags, in case the original vector had no report_quiesce.
+ */
+ want = engine->flags;
+ smp_rmb();
+ ops = engine->ops;
+
+ if (want & UTRACE_EVENT(QUIESCE)) {
+ if (finish_callback(task, utrace, report, engine,
+ (*ops->report_quiesce)(report->action,
+ engine, event)))
+ return NULL;
+
+ /*
+ * finish_callback() reset utrace->reporting after the
+ * quiesce callback. Now we set it again (as above)
+ * before re-examining engine->flags, which could have
+ * been changed synchronously by ->report_quiesce or
+ * asynchronously by utrace_control() or utrace_set_events().
+ */
+ utrace->reporting = engine;
+ smp_mb();
+ want = engine->flags;
+ }
+
+ if (want & ENGINE_STOP)
+ report->action = UTRACE_STOP;
+
+ if (want & event) {
+ report->spurious = false;
+ return ops;
+ }
+
+ utrace->reporting = NULL;
+ return NULL;
+}
+
+/*
+ * Do a normal reporting pass for engines interested in @event.
+ * @callback is the name of the member in the ops vector, and remaining
+ * args are the extras it takes after the standard three args.
+ */
+#define REPORT_CALLBACKS(rev, task, utrace, report, event, callback, ...) \
+ do { \
+ struct utrace_engine *engine; \
+ const struct utrace_engine_ops *ops; \
+ list_for_each_entry##rev(engine, &utrace->attached, entry) { \
+ ops = start_callback(utrace, report, engine, task, \
+ event); \
+ if (!ops) \
+ continue; \
+ finish_callback(task, utrace, report, engine, \
+ (*ops->callback)(__VA_ARGS__)); \
+ } \
+ } while (0)
+#define REPORT(task, utrace, report, event, callback, ...) \
+ do { \
+ start_report(utrace); \
+ REPORT_CALLBACKS(, task, utrace, report, event, callback, \
+ (report)->action, engine, ## __VA_ARGS__); \
+ finish_report(task, utrace, report, true); \
+ } while (0)
+
+/*
+ * Called iff UTRACE_EVENT(EXEC) flag is set.
+ */
+void utrace_report_exec(struct linux_binfmt *fmt, struct linux_binprm *bprm,
+ struct pt_regs *regs)
+{
+ struct task_struct *task = current;
+ struct utrace *utrace = task_utrace_struct(task);
+ INIT_REPORT(report);
+
+ REPORT(task, utrace, &report, UTRACE_EVENT(EXEC),
+ report_exec, fmt, bprm, regs);
+}
+
+static u32 do_report_syscall_entry(struct pt_regs *regs,
+ struct task_struct *task,
+ struct utrace *utrace,
+ struct utrace_report *report,
+ u32 resume_report)
+{
+ start_report(utrace);
+ REPORT_CALLBACKS(_reverse, task, utrace, report,
+ UTRACE_EVENT(SYSCALL_ENTRY), report_syscall_entry,
+ resume_report | report->result | report->action,
+ engine, regs);
+ finish_report(task, utrace, report, false);
+
+ if (report->action != UTRACE_STOP)
+ return 0;
+
+ utrace_stop(task, utrace, report->resume_action);
+
+ if (fatal_signal_pending(task)) {
+ /*
+ * We are continuing despite UTRACE_STOP because of a
+ * SIGKILL. Don't let the system call actually proceed.
+ */
+ report->result = UTRACE_SYSCALL_ABORT;
+ } else if (utrace->resume <= UTRACE_REPORT) {
+ /*
+ * If we've been asked for another report after our stop,
+ * go back to report (and maybe stop) again before we run
+ * the system call. The second (and later) reports are
+ * marked with the UTRACE_SYSCALL_RESUMED flag so that
+ * engines know this is a second report at the same
+ * entry. This gives them the chance to examine the
+ * registers anew after they might have been changed
+ * while we were stopped.
+ */
+ report->detaches = false;
+ report->spurious = true;
+ report->action = report->resume_action = UTRACE_RESUME;
+ return UTRACE_SYSCALL_RESUMED;
+ }
+
+ return 0;
+}
+
+/*
+ * Called iff UTRACE_EVENT(SYSCALL_ENTRY) flag is set.
+ * Return true to prevent the system call.
+ */
+bool utrace_report_syscall_entry(struct pt_regs *regs)
+{
+ struct task_struct *task = current;
+ struct utrace *utrace = task_utrace_struct(task);
+ INIT_REPORT(report);
+ u32 resume_report = 0;
+
+ do {
+ resume_report = do_report_syscall_entry(regs, task, utrace,
+ &report, resume_report);
+ } while (resume_report);
+
+ return utrace_syscall_action(report.result) == UTRACE_SYSCALL_ABORT;
+}
+
+/*
+ * Called iff UTRACE_EVENT(SYSCALL_EXIT) flag is set.
+ */
+void utrace_report_syscall_exit(struct pt_regs *regs)
+{
+ struct task_struct *task = current;
+ struct utrace *utrace = task_utrace_struct(task);
+ INIT_REPORT(report);
+
+ REPORT(task, utrace, &report, UTRACE_EVENT(SYSCALL_EXIT),
+ report_syscall_exit, regs);
+}
+
+/*
+ * Called iff UTRACE_EVENT(CLONE) flag is set.
+ * This notification call blocks the wake_up_new_task call on the child.
+ * So we must not quiesce here. tracehook_report_clone_complete will do
+ * a quiescence check momentarily.
+ */
+void utrace_report_clone(unsigned long clone_flags, struct task_struct *child)
+{
+ struct task_struct *task = current;
+ struct utrace *utrace = task_utrace_struct(task);
+ INIT_REPORT(report);
+
+ /*
+ * We don't use the REPORT() macro here, because we need
+ * to clear utrace->cloning before finish_report().
+ * After finish_report(), utrace can be a stale pointer
+ * in cases when report.action is still UTRACE_RESUME.
+ */
+ start_report(utrace);
+ utrace->cloning = child;
+
+ REPORT_CALLBACKS(, task, utrace, &report,
+ UTRACE_EVENT(CLONE), report_clone,
+ report.action, engine, clone_flags, child);
+
+ utrace->cloning = NULL;
+ finish_report(task, utrace, &report, !(clone_flags & CLONE_VFORK));
+
+ /*
+ * For a vfork, we will go into an uninterruptible block waiting
+ * for the child. We need UTRACE_STOP to happen before this, not
+ * after. For CLONE_VFORK, utrace_finish_vfork() will be called.
+ */
+ if (report.action == UTRACE_STOP && (clone_flags & CLONE_VFORK)) {
+ spin_lock(&utrace->lock);
+ utrace->vfork_stop = 1;
+ spin_unlock(&utrace->lock);
+ }
+}
+
+/*
+ * We're called after utrace_report_clone() for a CLONE_VFORK.
+ * If UTRACE_STOP was left from the clone report, we stop here.
+ * After this, we'll enter the uninterruptible wait_for_completion()
+ * waiting for the child.
+ */
+void utrace_finish_vfork(struct task_struct *task)
+{
+ struct utrace *utrace = task_utrace_struct(task);
+
+ if (utrace->vfork_stop) {
+ spin_lock(&utrace->lock);
+ utrace->vfork_stop = 0;
+ spin_unlock(&utrace->lock);
+ utrace_stop(task, utrace, UTRACE_RESUME); /* XXX */
+ }
+}
+
+/*
+ * Called iff UTRACE_EVENT(JCTL) flag is set.
+ *
+ * Called with siglock held.
+ */
+void utrace_report_jctl(int notify, int what)
+{
+ struct task_struct *task = current;
+ struct utrace *utrace = task_utrace_struct(task);
+ INIT_REPORT(report);
+
+ spin_unlock_irq(&task->sighand->siglock);
+
+ REPORT(task, utrace, &report, UTRACE_EVENT(JCTL),
+ report_jctl, what, notify);
+
+ spin_lock_irq(&task->sighand->siglock);
+}
+
+/*
+ * Called iff UTRACE_EVENT(EXIT) flag is set.
+ */
+void utrace_report_exit(long *exit_code)
+{
+ struct task_struct *task = current;
+ struct utrace *utrace = task_utrace_struct(task);
+ INIT_REPORT(report);
+ long orig_code = *exit_code;
+
+ REPORT(task, utrace, &report, UTRACE_EVENT(EXIT),
+ report_exit, orig_code, exit_code);
+
+ if (report.action == UTRACE_STOP)
+ utrace_stop(task, utrace, report.resume_action);
+}
+
+/*
+ * Called iff UTRACE_EVENT(DEATH) or UTRACE_EVENT(QUIESCE) flag is set.
+ *
+ * It is always possible that we are racing with utrace_release_task here.
+ * For this reason, utrace_release_task checks for the event bits that get
+ * us here, and delays its cleanup for us to do.
+ */
+void utrace_report_death(struct task_struct *task, struct utrace *utrace,
+ bool group_dead, int signal)
+{
+ INIT_REPORT(report);
+
+ BUG_ON(!task->exit_state);
+
+ /*
+ * We are presently considered "quiescent"--which is accurate
+ * inasmuch as we won't run any more user instructions ever again.
+ * But for utrace_control and utrace_set_events to be robust, they
+ * must be sure whether or not we will run any more callbacks. If
+ * a call comes in before we do, taking the lock here synchronizes
+ * us so we don't run any callbacks just disabled. Calls that come
+ * in while we're running the callbacks will see the exit.death
+ * flag and know that we are not yet fully quiescent for purposes
+ * of detach bookkeeping.
+ */
+ spin_lock(&utrace->lock);
+ BUG_ON(utrace->death);
+ utrace->death = 1;
+ utrace->resume = UTRACE_RESUME;
+ splice_attaching(utrace);
+ spin_unlock(&utrace->lock);
+
+ REPORT_CALLBACKS(, task, utrace, &report, UTRACE_EVENT(DEATH),
+ report_death, engine, group_dead, signal);
+
+ utrace_maybe_reap(task, utrace, false);
+}
+
+/*
+ * Finish the last reporting pass before returning to user mode.
+ */
+static void finish_resume_report(struct task_struct *task,
+ struct utrace *utrace,
+ struct utrace_report *report)
+{
+ finish_report_reset(task, utrace, report);
+
+ switch (report->action) {
+ case UTRACE_STOP:
+ utrace_stop(task, utrace, report->resume_action);
+ break;
+
+ case UTRACE_INTERRUPT:
+ if (!signal_pending(task))
+ set_tsk_thread_flag(task, TIF_SIGPENDING);
+ break;
+
+ case UTRACE_BLOCKSTEP:
+ if (likely(arch_has_block_step())) {
+ user_enable_block_step(task);
+ break;
+ }
+
+ /*
+ * This means some callback is to blame for failing
+ * to check arch_has_block_step() itself. Warn and
+ * then fall through to treat it as SINGLESTEP.
+ */
+ WARN(1, "UTRACE_BLOCKSTEP when !arch_has_block_step()");
+
+ case UTRACE_SINGLESTEP:
+ if (likely(arch_has_single_step())) {
+ user_enable_single_step(task);
+ } else {
+ /*
+ * This means some callback is to blame for failing
+ * to check arch_has_single_step() itself. Spew
+ * about it so the loser will fix his module.
+ */
+ WARN(1,
+ "UTRACE_SINGLESTEP when !arch_has_single_step()");
+ }
+ break;
+
+ case UTRACE_REPORT:
+ case UTRACE_RESUME:
+ default:
+ user_disable_single_step(task);
+ break;
+ }
+}
+
+/*
+ * This is called when TIF_NOTIFY_RESUME had been set (and is now clear).
+ * We are close to user mode, and this is the place to report or stop.
+ * When we return, we're going to user mode or into the signals code.
+ */
+void utrace_resume(struct task_struct *task, struct pt_regs *regs)
+{
+ struct utrace *utrace = task_utrace_struct(task);
+ INIT_REPORT(report);
+ struct utrace_engine *engine;
+
+ /*
+ * Some machines get here with interrupts disabled. The same arch
+ * code path leads to calling into get_signal_to_deliver(), which
+ * implicitly reenables them by virtue of spin_unlock_irq.
+ */
+ local_irq_enable();
+
+ /*
+ * If this flag is still set it's because there was a signal
+ * handler setup done but no report_signal following it. Clear
+ * the flag before we get to user so it doesn't confuse us later.
+ */
+ if (unlikely(utrace->signal_handler)) {
+ spin_lock(&utrace->lock);
+ utrace->signal_handler = 0;
+ spin_unlock(&utrace->lock);
+ }
+
+ /*
+ * Update our bookkeeping even if there are no callbacks made here.
+ */
+ report.action = start_report(utrace);
+
+ switch (report.action) {
+ case UTRACE_RESUME:
+ /*
+ * Anything we might have done was already handled by
+ * utrace_get_signal(), or this is an entirely spurious
+ * call. (The arch might use TIF_NOTIFY_RESUME for other
+ * purposes as well as calling us.)
+ */
+ return;
+ case UTRACE_REPORT:
+ if (unlikely(!(task->utrace_flags & UTRACE_EVENT(QUIESCE))))
+ break;
+ /*
+ * Do a simple reporting pass, with no specific
+ * callback after report_quiesce.
+ */
+ report.action = UTRACE_RESUME;
+ list_for_each_entry(engine, &utrace->attached, entry)
+ start_callback(utrace, &report, engine, task, 0);
+ break;
+ default:
+ /*
+ * Even if this report was truly spurious, there is no need
+ * for utrace_reset() now. TIF_NOTIFY_RESUME was already
+ * cleared--it doesn't stay spuriously set.
+ */
+ report.spurious = false;
+ break;
+ }
+
+ /*
+ * Finish the report and either stop or get ready to resume.
+ * If utrace->resume was not UTRACE_REPORT, this applies its
+ * effect now (i.e. step or interrupt).
+ */
+ finish_resume_report(task, utrace, &report);
+}
+
+/*
+ * Return true if current has forced signal_pending().
+ *
+ * This is called only when current->utrace_flags is nonzero, so we know
+ * that current->utrace must be set. It's not inlined in tracehook.h
+ * just so that struct utrace can stay opaque outside this file.
+ */
+bool utrace_interrupt_pending(void)
+{
+ return task_utrace_struct(current)->resume == UTRACE_INTERRUPT;
+}
+
+/*
+ * Take the siglock and push @info back on our queue.
+ * Returns with @task->sighand->siglock held.
+ */
+static void push_back_signal(struct task_struct *task, siginfo_t *info)
+ __acquires(task->sighand->siglock)
+{
+ struct sigqueue *q;
+
+ if (unlikely(!info->si_signo)) { /* Oh, a wise guy! */
+ spin_lock_irq(&task->sighand->siglock);
+ return;
+ }
+
+ q = sigqueue_alloc();
+ if (likely(q)) {
+ q->flags = 0;
+ copy_siginfo(&q->info, info);
+ }
+
+ spin_lock_irq(&task->sighand->siglock);
+
+ sigaddset(&task->pending.signal, info->si_signo);
+ if (likely(q))
+ list_add(&q->list, &task->pending.list);
+
+ set_tsk_thread_flag(task, TIF_SIGPENDING);
+}
+
+/*
+ * This is the hook from the signals code, called with the siglock held.
+ * Here is the ideal place to stop. We also dequeue and intercept signals.
+ */
+int utrace_get_signal(struct task_struct *task, struct pt_regs *regs,
+ siginfo_t *info, struct k_sigaction *return_ka)
+ __releases(task->sighand->siglock)
+ __acquires(task->sighand->siglock)
+{
+ struct utrace *utrace;
+ struct k_sigaction *ka;
+ INIT_REPORT(report);
+ struct utrace_engine *engine;
+ const struct utrace_engine_ops *ops;
+ unsigned long event, want;
+ u32 ret;
+ int signr;
+
+ utrace = task_utrace_struct(task);
+ if (utrace->resume < UTRACE_RESUME ||
+ utrace->pending_attach || utrace->signal_handler) {
+ enum utrace_resume_action resume;
+
+ /*
+ * We've been asked for an explicit report before we
+ * even check for pending signals.
+ */
+
+ spin_unlock_irq(&task->sighand->siglock);
+
+ spin_lock(&utrace->lock);
+
+ splice_attaching(utrace);
+
+ report.result = utrace->signal_handler ?
+ UTRACE_SIGNAL_HANDLER : UTRACE_SIGNAL_REPORT;
+ utrace->signal_handler = 0;
+
+ resume = utrace->resume;
+ utrace->resume = UTRACE_RESUME;
+
+ spin_unlock(&utrace->lock);
+
+ /*
+ * Make sure signal_pending() only returns true
+ * if there are real signals pending.
+ */
+ if (signal_pending(task)) {
+ spin_lock_irq(&task->sighand->siglock);
+ recalc_sigpending();
+ spin_unlock_irq(&task->sighand->siglock);
+ }
+
+ if (resume > UTRACE_REPORT) {
+ /*
+ * We only got here to process utrace->resume.
+ * Despite no callbacks, this report is not spurious.
+ */
+ report.action = resume;
+ report.spurious = false;
+ finish_resume_report(task, utrace, &report);
+ return -1;
+ } else if (!(task->utrace_flags & UTRACE_EVENT(QUIESCE))) {
+ /*
+ * We only got here to clear utrace->signal_handler.
+ */
+ return -1;
+ }
+
+ /*
+ * Do a reporting pass for no signal, just for EVENT(QUIESCE).
+ * The engine callbacks can fill in *info and *return_ka.
+ * We'll pass NULL for the @orig_ka argument to indicate
+ * that there was no original signal.
+ */
+ event = 0;
+ ka = NULL;
+ memset(return_ka, 0, sizeof *return_ka);
+ } else if (!(task->utrace_flags & UTRACE_EVENT_SIGNAL_ALL) ||
+ unlikely(task->signal->group_stop_count)) {
+ /*
+ * If no engine is interested in intercepting signals or
+ * we must stop, let the caller just dequeue them normally
+ * or participate in group-stop.
+ */
+ return 0;
+ } else {
+ /*
+ * Steal the next signal so we can let tracing engines
+ * examine it. From the signal number and sigaction,
+ * determine what normal delivery would do. If no
+ * engine perturbs it, we'll do that by returning the
+ * signal number after setting *return_ka.
+ */
+ signr = dequeue_signal(task, &task->blocked, info);
+ if (signr == 0)
+ return signr;
+ BUG_ON(signr != info->si_signo);
+
+ ka = &task->sighand->action[signr - 1];
+ *return_ka = *ka;
+
+ /*
+ * We are never allowed to interfere with SIGKILL.
+ * Just punt after filling in *return_ka for our caller.
+ */
+ if (signr == SIGKILL)
+ return signr;
+
+ if (ka->sa.sa_handler == SIG_IGN) {
+ event = UTRACE_EVENT(SIGNAL_IGN);
+ report.result = UTRACE_SIGNAL_IGN;
+ } else if (ka->sa.sa_handler != SIG_DFL) {
+ event = UTRACE_EVENT(SIGNAL);
+ report.result = UTRACE_SIGNAL_DELIVER;
+ } else if (sig_kernel_coredump(signr)) {
+ event = UTRACE_EVENT(SIGNAL_CORE);
+ report.result = UTRACE_SIGNAL_CORE;
+ } else if (sig_kernel_ignore(signr)) {
+ event = UTRACE_EVENT(SIGNAL_IGN);
+ report.result = UTRACE_SIGNAL_IGN;
+ } else if (signr == SIGSTOP) {
+ event = UTRACE_EVENT(SIGNAL_STOP);
+ report.result = UTRACE_SIGNAL_STOP;
+ } else if (sig_kernel_stop(signr)) {
+ event = UTRACE_EVENT(SIGNAL_STOP);
+ report.result = UTRACE_SIGNAL_TSTP;
+ } else {
+ event = UTRACE_EVENT(SIGNAL_TERM);
+ report.result = UTRACE_SIGNAL_TERM;
+ }
+
+ /*
+ * Now that we know what event type this signal is, we
+ * can short-circuit if no engines care about those.
+ */
+ if ((task->utrace_flags & (event | UTRACE_EVENT(QUIESCE))) == 0)
+ return signr;
+
+ /*
+ * We have some interested engines, so tell them about
+ * the signal and let them change its disposition.
+ */
+ spin_unlock_irq(&task->sighand->siglock);
+ }
+
+ /*
+ * This reporting pass chooses what signal disposition we'll act on.
+ */
+ list_for_each_entry(engine, &utrace->attached, entry) {
+ /*
+ * See start_callback() comment about this barrier.
+ */
+ utrace->reporting = engine;
+ smp_mb();
+
+ /*
+ * This pairs with the barrier in mark_engine_detached(),
+ * see start_callback() comments.
+ */
+ want = engine->flags;
+ smp_rmb();
+ ops = engine->ops;
+
+ if ((want & (event | UTRACE_EVENT(QUIESCE))) == 0) {
+ utrace->reporting = NULL;
+ continue;
+ }
+
+ if (ops->report_signal)
+ ret = (*ops->report_signal)(
+ report.result | report.action, engine,
+ regs, info, ka, return_ka);
+ else
+ ret = (report.result | (*ops->report_quiesce)(
+ report.action, engine, event));
+
+ /*
+ * Avoid a tight loop reporting again and again if some
+ * engine is too stupid.
+ */
+ switch (utrace_resume_action(ret)) {
+ default:
+ break;
+ case UTRACE_INTERRUPT:
+ case UTRACE_REPORT:
+ ret = (ret & ~UTRACE_RESUME_MASK) | UTRACE_RESUME;
+ break;
+ }
+
+ finish_callback(task, utrace, &report, engine, ret);
+ }
+
+ /*
+ * We express the chosen action to the signals code in terms
+ * of a representative signal whose default action does it.
+ * Our caller uses our return value (signr) to decide what to
+ * do, but uses info->si_signo as the signal number to report.
+ */
+ switch (utrace_signal_action(report.result)) {
+ case UTRACE_SIGNAL_TERM:
+ signr = SIGTERM;
+ break;
+
+ case UTRACE_SIGNAL_CORE:
+ signr = SIGQUIT;
+ break;
+
+ case UTRACE_SIGNAL_STOP:
+ signr = SIGSTOP;
+ break;
+
+ case UTRACE_SIGNAL_TSTP:
+ signr = SIGTSTP;
+ break;
+
+ case UTRACE_SIGNAL_DELIVER:
+ signr = info->si_signo;
+
+ if (return_ka->sa.sa_handler == SIG_DFL) {
+ /*
+ * We'll do signr's normal default action.
+ * For ignore, we'll fall through below.
+ * For stop/death, break locks and returns it.
+ */
+ if (likely(signr) && !sig_kernel_ignore(signr))
+ break;
+ } else if (return_ka->sa.sa_handler != SIG_IGN &&
+ likely(signr)) {
+ /*
+ * Complete the bookkeeping after the report.
+ * The handler will run. If an engine wanted to
+ * stop or step, then make sure we do another
+ * report after signal handler setup.
+ */
+ if (report.action != UTRACE_RESUME)
+ report.action = UTRACE_INTERRUPT;
+ finish_report(task, utrace, &report, true);
+
+ if (unlikely(report.result & UTRACE_SIGNAL_HOLD))
+ push_back_signal(task, info);
+ else
+ spin_lock_irq(&task->sighand->siglock);
+
+ /*
+ * We do the SA_ONESHOT work here since the
+ * normal path will only touch *return_ka now.
+ */
+ if (unlikely(return_ka->sa.sa_flags & SA_ONESHOT)) {
+ return_ka->sa.sa_flags &= ~SA_ONESHOT;
+ if (likely(valid_signal(signr))) {
+ ka = &task->sighand->action[signr - 1];
+ ka->sa.sa_handler = SIG_DFL;
+ }
+ }
+
+ return signr;
+ }
+
+ /* Fall through for an ignored signal. */
+
+ case UTRACE_SIGNAL_IGN:
+ case UTRACE_SIGNAL_REPORT:
+ default:
+ /*
+ * If the signal is being ignored, then we are on the way
+ * directly back to user mode. We can stop here, or step,
+ * as in utrace_resume(), above. After we've dealt with that,
+ * our caller will relock and come back through here.
+ */
+ finish_resume_report(task, utrace, &report);
+
+ if (unlikely(fatal_signal_pending(task))) {
+ /*
+ * The only reason we woke up now was because of a
+ * SIGKILL. Don't do normal dequeuing in case it
+ * might get a signal other than SIGKILL. That would
+ * perturb the death state so it might differ from
+ * what the debugger would have allowed to happen.
+ * Instead, pluck out just the SIGKILL to be sure
+ * we'll die immediately with nothing else different
+ * from the quiescent state the debugger wanted us in.
+ */
+ sigset_t sigkill_only;
+ siginitsetinv(&sigkill_only, sigmask(SIGKILL));
+ spin_lock_irq(&task->sighand->siglock);
+ signr = dequeue_signal(task, &sigkill_only, info);
+ BUG_ON(signr != SIGKILL);
+ *return_ka = task->sighand->action[SIGKILL - 1];
+ return signr;
+ }
+
+ if (unlikely(report.result & UTRACE_SIGNAL_HOLD)) {
+ push_back_signal(task, info);
+ spin_unlock_irq(&task->sighand->siglock);
+ }
+
+ return -1;
+ }
+
+ /*
+ * Complete the bookkeeping after the report.
+ * This sets utrace->resume if UTRACE_STOP was used.
+ */
+ finish_report(task, utrace, &report, true);
+
+ return_ka->sa.sa_handler = SIG_DFL;
+
+ /*
+ * If this signal is fatal, si_signo gets through as exit_code.
+ * We can't allow a completely bogus value there or else core
+ * kernel code can freak out. (If an engine wants to control
+ * the exit_code value exactly, it can do so in report_exit.)
+ * We'll produce a big complaint in dmesg, but won't crash.
+ * That's nicer for debugging your utrace engine.
+ */
+ if (unlikely(info->si_signo & 0x80)) {
+ WARN(1, "utrace engine left bogus si_signo value!");
+ info->si_signo = SIGTRAP;
+ }
+
+ if (unlikely(report.result & UTRACE_SIGNAL_HOLD))
+ push_back_signal(task, info);
+ else
+ spin_lock_irq(&task->sighand->siglock);
+
+ if (sig_kernel_stop(signr))
+ task->signal->flags |= SIGNAL_STOP_DEQUEUED;
+
+ return signr;
+}
+
+/*
+ * This gets called after a signal handler has been set up.
+ * We set a flag so the next report knows it happened.
+ * If we're already stepping, make sure we do a report_signal.
+ * If not, make sure we get into utrace_resume() where we can
+ * clear the signal_handler flag before resuming.
+ */
+void utrace_signal_handler(struct task_struct *task, int stepping)
+{
+ struct utrace *utrace = task_utrace_struct(task);
+
+ spin_lock(&utrace->lock);
+
+ utrace->signal_handler = 1;
+ if (utrace->resume > UTRACE_INTERRUPT) {
+ if (stepping) {
+ utrace->resume = UTRACE_INTERRUPT;
+ set_tsk_thread_flag(task, TIF_SIGPENDING);
+ } else if (utrace->resume == UTRACE_RESUME) {
+ set_tsk_thread_flag(task, TIF_NOTIFY_RESUME);
+ }
+ }
+
+ spin_unlock(&utrace->lock);
+}
+
+/**
+ * utrace_prepare_examine - prepare to examine thread state
+ * @target: thread of interest, a &struct task_struct pointer
+ * @engine: engine pointer returned by utrace_attach_task()
+ * @exam: temporary state, a &struct utrace_examiner pointer
+ *
+ * This call prepares to safely examine the thread @target using
+ * &struct user_regset calls, or direct access to thread-synchronous fields.
+ *
+ * When @target is current, this call is superfluous. When @target is
+ * another thread, it must be held stopped via %UTRACE_STOP by @engine.
+ *
+ * This call may block the caller until @target stays stopped, so it must
+ * be called only after the caller is sure @target is about to unschedule.
+ * This means a zero return from a utrace_control() call on @engine giving
+ * %UTRACE_STOP, or a report_quiesce() or report_signal() callback to
+ * @engine that used %UTRACE_STOP in its return value.
+ *
+ * Returns -%ESRCH if @target is dead or -%EINVAL if %UTRACE_STOP was
+ * not used. If @target has started running again despite %UTRACE_STOP
+ * (for %SIGKILL or a spurious wakeup), this call returns -%EAGAIN.
+ *
+ * When this call returns zero, it's safe to use &struct user_regset
+ * calls and task_user_regset_view() on @target and to examine some of
+ * its fields directly. When the examination is complete, a
+ * utrace_finish_examine() call must follow to check whether it was
+ * completed safely.
+ */
+int utrace_prepare_examine(struct task_struct *target,
+ struct utrace_engine *engine,
+ struct utrace_examiner *exam)
+{
+ int ret = 0;
+
+ if (unlikely(target == current))
+ return 0;
+
+ rcu_read_lock();
+ if (unlikely(!engine_wants_stop(engine)))
+ ret = -EINVAL;
+ else if (unlikely(target->exit_state))
+ ret = -ESRCH;
+ else {
+ exam->state = target->state;
+ if (unlikely(exam->state == TASK_RUNNING))
+ ret = -EAGAIN;
+ else
+ get_task_struct(target);
+ }
+ rcu_read_unlock();
+
+ if (likely(!ret)) {
+ exam->ncsw = wait_task_inactive(target, exam->state);
+ put_task_struct(target);
+ if (unlikely(!exam->ncsw))
+ ret = -EAGAIN;
+ }
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(utrace_prepare_examine);
+
+/**
+ * utrace_finish_examine - complete an examination of thread state
+ * @target: thread of interest, a &struct task_struct pointer
+ * @engine: engine pointer returned by utrace_attach_task()
+ * @exam: pointer passed to utrace_prepare_examine() call
+ *
+ * This call completes an examination on the thread @target begun by a
+ * paired utrace_prepare_examine() call with the same arguments that
+ * returned success (zero).
+ *
+ * When @target is current, this call is superfluous. When @target is
+ * another thread, this returns zero if @target has remained unscheduled
+ * since the paired utrace_prepare_examine() call returned zero.
+ *
+ * When this returns an error, any examination done since the paired
+ * utrace_prepare_examine() call is unreliable and the data extracted
+ * should be discarded. The error is -%EINVAL if @engine is not
+ * keeping @target stopped, or -%EAGAIN if @target woke up unexpectedly.
+ */
+int utrace_finish_examine(struct task_struct *target,
+ struct utrace_engine *engine,
+ struct utrace_examiner *exam)
+{
+ int ret = 0;
+
+ if (unlikely(target == current))
+ return 0;
+
+ rcu_read_lock();
+ if (unlikely(!engine_wants_stop(engine)))
+ ret = -EINVAL;
+ else if (unlikely(target->state != exam->state))
+ ret = -EAGAIN;
+ else
+ get_task_struct(target);
+ rcu_read_unlock();
+
+ if (likely(!ret)) {
+ unsigned long ncsw = wait_task_inactive(target, exam->state);
+ if (unlikely(ncsw != exam->ncsw))
+ ret = -EAGAIN;
+ put_task_struct(target);
+ }
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(utrace_finish_examine);
+
+/*
+ * This is declared in linux/regset.h and defined in machine-dependent
+ * code. We put the export here to ensure no machine forgets it.
+ */
+EXPORT_SYMBOL_GPL(task_user_regset_view);
+
+/*
+ * Called with rcu_read_lock() held.
+ */
+void task_utrace_proc_status(struct seq_file *m, struct task_struct *p)
+{
+ seq_printf(m, "Utrace:\t%lx\n", p->utrace_flags);
+}
--
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