linux-kernel - [PATCH 0/4] [GIT PULL] tracing/rcu: Fix save_stack

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Message-Id: <20170923205621.811805556@goodmis.org>
Date:   Sat, 23 Sep 2017 16:56:21 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH 0/4] [GIT PULL] tracing/rcu: Fix save_stack_trace() called when RCU is not watching

Linus,

Stack tracing and RCU has been having issues with each other and lockdep
has been pointing out constant problems. The changes have been going into
the stack tracer, but it has been discovered that the problem isn't
with the stack tracer itself, but it is with calling save_stack_trace()
from within the internals of RCU. The stack tracer is the one that
can trigger the issue the easiest, but examining the problem further,
it could also happen from a WARN() in the wrong place, or even if
an NMI happened in this area and it did an rcu_read_lock().

The critical area is where RCU is not watching. Which can happen while
going to and from idle, or bringing up or taking down a CPU.

The final fix was to put the protection in kernel_text_address() as it
is the one that requires RCU to be watching while doing the stack trace.

To make this work properly, Paul had to allow rcu_irq_enter() happen after
rcu_nmi_enter(). This should have been done anyway, since an NMI can
page fault (reading vmalloc area), and a page fault triggers rcu_irq_enter().

One patch is just a consolidation of code so that the fix only needed
to be done in one location.

Please pull the latest trace-v4.14-rc1-2 tree, which can be found at:

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
trace-v4.14-rc1-2

Tag SHA1: cdd226e99fbb8f22e5317e7968b37387108ce568
Head SHA1: 15516c89acce948debc4c598e03c3fee53045797

Paul E. McKenney (1):
      rcu: Allow for page faults in NMI handlers

Steven Rostedt (VMware) (3):
      extable: Consolidate *kernel_text_address() functions
      extable: Enable RCU if it is not watching in kernel_text_address()
      tracing: Remove RCU work arounds from stack tracer

----
 kernel/extable.c           | 45 +++++++++++++++++++++++++++++++--------------
 kernel/rcu/tree.c          | 10 ++++++++++
 kernel/trace/trace_stack.c | 15 ---------------
 3 files changed, 41 insertions(+), 29 deletions(-)