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Message-Id: <200702181956.11273.rjw@sisk.pl>
Date: Sun, 18 Feb 2007 19:56:10 +0100
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Oleg Nesterov <oleg@...sign.ru>
Cc: ego@...ibm.com, akpm@...l.org, paulmck@...ibm.com, mingo@...e.hu,
vatsa@...ibm.com, dipankar@...ibm.com,
venkatesh.pallipadi@...el.com, linux-kernel@...r.kernel.org,
Pavel Machek <pavel@....cz>
Subject: Re: freezer problems
On Sunday, 18 February 2007 15:52, Oleg Nesterov wrote:
> On 02/18, Rafael J. Wysocki wrote:
> >
> > On Sunday, 18 February 2007 12:31, Oleg Nesterov wrote:
> > > > >
> > > > > However, this means that sys_vfork() makes impossible to freeze processes
> > > > > until child exits/execs. Not good.
> > > >
> > > I forgot to say that we have another problem: coredumping.
> > >
> > > A thread which does do_coredump() send SIGKILL to ->mm users, and sleeps
> > > on ->mm->core_startup_done. Now it can't be frozen if sub-thread goes to
> > > refrigerator. I think this could be solved easily if we add a check to
> > > refrigerator() as you suggested for ->vfork_donw.
> > >
> > > > I think the real solution would be to use an interruptible completion in the
> > > > vfork code. It was discussed some time ago and, IIRC, Ingo had an experimental
> > > > patch that implemented it. Still, for the suspend this really is not an issue
> > > > in practice, so it wasn't merged.
> > >
> > > It is not (afaics) so trivial to do rightly, and with this change the parent
> > > will be seen as TASK_INTERRUPTIBLE even without freezer in progress.
> > >
> > > A very vague idea: what if parent will do
> > >
> > > current->flags |= PF_PLEASE_CONSIDER_ME_AS_FROZEN_BUT_SET_TIF_FREEZE
> > > wait_for_completion(&vfork);
> > > try_to_freeze();
> > >
> > > ?
> >
> > This should work,
>
> Good. So try_to_freeze_tasks() can forget about "if (!p->vfork_done)" check.
> This needs more thinking, of course. For example, thaw_process() should be
> carefull to clear TIF_FREEZE if we have the new flag set, but not PF_FROZEN.
> frozen() should be changed to return true if PF_NEW_FLAG && TIF_FREEZE, but
> it also called by refrigerator.
>
> But IF we really can do this, it will be a general solution.
Appended is a patch that does something along these lines. The necessary
thread_info flags are defined for i386 and x86_64, for now.
Greetings,
Rafael
include/asm-i386/thread_info.h | 2 ++
include/asm-x86_64/thread_info.h | 2 ++
include/linux/freezer.h | 24 ++++++++++++++++++++++++
kernel/fork.c | 4 ++++
kernel/power/process.c | 24 +++++++++---------------
5 files changed, 41 insertions(+), 15 deletions(-)
Index: linux-2.6.20-mm2/include/asm-i386/thread_info.h
===================================================================
--- linux-2.6.20-mm2.orig/include/asm-i386/thread_info.h 2007-02-18 19:49:34.000000000 +0100
+++ linux-2.6.20-mm2/include/asm-i386/thread_info.h 2007-02-18 19:50:37.000000000 +0100
@@ -135,6 +135,7 @@ static inline struct thread_info *curren
#define TIF_IO_BITMAP 18 /* uses I/O bitmap */
#define TIF_FREEZE 19 /* is freezing for suspend */
#define TIF_FORCED_TF 20 /* true if TF in eflags artificially */
+#define TIF_FREEZER_SKIP 21 /* task freezer should not count us */
#define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)
#define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
@@ -149,6 +150,7 @@ static inline struct thread_info *curren
#define _TIF_IO_BITMAP (1<<TIF_IO_BITMAP)
#define _TIF_FREEZE (1<<TIF_FREEZE)
#define _TIF_FORCED_TF (1<<TIF_FORCED_TF)
+#define _TIF_FREEZER_SKIP (1<<TIF_FREEZER_SKIP)
/* work to do on interrupt/exception return */
#define _TIF_WORK_MASK \
Index: linux-2.6.20-mm2/include/asm-x86_64/thread_info.h
===================================================================
--- linux-2.6.20-mm2.orig/include/asm-x86_64/thread_info.h 2007-02-18 19:49:34.000000000 +0100
+++ linux-2.6.20-mm2/include/asm-x86_64/thread_info.h 2007-02-18 19:50:37.000000000 +0100
@@ -123,6 +123,7 @@ static inline struct thread_info *stack_
#define TIF_DEBUG 21 /* uses debug registers */
#define TIF_IO_BITMAP 22 /* uses I/O bitmap */
#define TIF_FREEZE 23 /* is freezing for suspend */
+#define TIF_FREEZER_SKIP 24 /* task freezer should not count us */
#define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)
#define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
@@ -140,6 +141,7 @@ static inline struct thread_info *stack_
#define _TIF_DEBUG (1<<TIF_DEBUG)
#define _TIF_IO_BITMAP (1<<TIF_IO_BITMAP)
#define _TIF_FREEZE (1<<TIF_FREEZE)
+#define _TIF_FREEZER_SKIP (1<<TIF_FREEZER_SKIP)
/* work to do on interrupt/exception return */
#define _TIF_WORK_MASK \
Index: linux-2.6.20-mm2/include/linux/freezer.h
===================================================================
--- linux-2.6.20-mm2.orig/include/linux/freezer.h 2007-02-18 19:49:34.000000000 +0100
+++ linux-2.6.20-mm2/include/linux/freezer.h 2007-02-18 19:50:37.000000000 +0100
@@ -36,6 +36,30 @@ static inline void do_not_freeze(struct
}
/*
+ * Tell the freezer not to count this task as freezeable
+ */
+static inline void freezer_do_not_count(struct task_struct *p)
+{
+ set_tsk_thread_flag(p, TIF_FREEZER_SKIP);
+}
+
+/*
+ * Tell the freezer to count this task as freezeable
+ */
+static inline void freezer_count(struct task_struct *p)
+{
+ clear_tsk_thread_flag(p, TIF_FREEZER_SKIP);
+}
+
+/*
+ * Check if the task should be counted as freezeable by the freezer
+ */
+static inline int freezer_should_skip(struct task_struct *p)
+{
+ return test_tsk_thread_flag(p, TIF_FREEZER_SKIP);
+}
+
+/*
* Wake up a frozen process
*/
static inline int thaw_process(struct task_struct *p)
Index: linux-2.6.20-mm2/kernel/fork.c
===================================================================
--- linux-2.6.20-mm2.orig/kernel/fork.c 2007-02-18 19:49:34.000000000 +0100
+++ linux-2.6.20-mm2/kernel/fork.c 2007-02-18 19:50:37.000000000 +0100
@@ -50,6 +50,7 @@
#include <linux/taskstats_kern.h>
#include <linux/random.h>
#include <linux/ptrace.h>
+#include <linux/freezer.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -1393,7 +1394,10 @@ long do_fork(unsigned long clone_flags,
tracehook_report_clone_complete(clone_flags, nr, p);
if (clone_flags & CLONE_VFORK) {
+ freezer_do_not_count(current);
wait_for_completion(&vfork);
+ try_to_freeze();
+ freezer_count(current);
tracehook_report_vfork_done(p, nr);
}
} else {
Index: linux-2.6.20-mm2/kernel/power/process.c
===================================================================
--- linux-2.6.20-mm2.orig/kernel/power/process.c 2007-02-18 19:49:34.000000000 +0100
+++ linux-2.6.20-mm2/kernel/power/process.c 2007-02-18 19:50:37.000000000 +0100
@@ -117,22 +117,12 @@ static unsigned int try_to_freeze_tasks(
cancel_freezing(p);
continue;
}
- if (is_user_space(p)) {
- if (!freeze_user_space)
- continue;
-
- /* Freeze the task unless there is a vfork
- * completion pending
- */
- if (!p->vfork_done)
- freeze_process(p);
- } else {
- if (freeze_user_space)
- continue;
+ if (is_user_space(p) == !freeze_user_space)
+ continue;
- freeze_process(p);
- }
- todo++;
+ freeze_process(p);
+ if (!freezer_should_skip(p))
+ todo++;
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
yield(); /* Yield is okay here */
@@ -199,6 +189,10 @@ static void thaw_tasks(int thaw_user_spa
read_lock(&tasklist_lock);
do_each_thread(g, p) {
+ if (freezer_should_skip(p))
+ cancel_freezing(p);
+ } while_each_thread(g, p);
+ do_each_thread(g, p) {
if (!freezeable(p))
continue;
-
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