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oom, suspend: fix oom_reaper vs. oom_killer_disable race

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Tetsuo has reported the following potential oom_killer_disable vs.
oom_reaper race:

 (1) freeze_processes() starts freezing user space threads.
 (2) Somebody (maybe a kenrel thread) calls out_of_memory().
 (3) The OOM killer calls mark_oom_victim() on a user space thread
     P1 which is already in __refrigerator().
 (4) oom_killer_disable() sets oom_killer_disabled = true.
 (5) P1 leaves __refrigerator() and enters do_exit().
 (6) The OOM reaper calls exit_oom_victim(P1) before P1 can call
     exit_oom_victim(P1).
 (7) oom_killer_disable() returns while P1 not yet finished
 (8) P1 perform IO/interfere with the freezer.

This situation is unfortunate.  We cannot move oom_killer_disable after
all the freezable kernel threads are frozen because the oom victim might
depend on some of those kthreads to make a forward progress to exit so
we could deadlock.  It is also far from trivial to teach the oom_reaper
to not call exit_oom_victim() because then we would lose a guarantee of
the OOM killer and oom_killer_disable forward progress because
exit_mm->mmput might block and never call exit_oom_victim.

It seems the easiest way forward is to workaround this race by calling
try_to_freeze_tasks again after oom_killer_disable.  This will make sure
that all the tasks are frozen or it bails out.

Fixes: 449d777d7ad6 ("mm, oom_reaper: clear TIF_MEMDIE for all tasks queued for oom_reaper")
Link: http://lkml.kernel.org/r/1466597634-16199-1-git-send-email-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michal Hocko 2016-06-24 14:50:16 -07:00 committed by Linus Torvalds
parent 7186ee06b6
commit 7407054209
1 changed files with 12 additions and 0 deletions
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12
kernel/power/process.c
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@ -146,6 +146,18 @@ int freeze_processes(void)
if (!error && !oom_killer_disable()) if (!error && !oom_killer_disable())
error = -EBUSY; error = -EBUSY;
/*
* There is a hard to fix race between oom_reaper kernel thread
* and oom_killer_disable. oom_reaper calls exit_oom_victim
* before the victim reaches exit_mm so try to freeze all the tasks
* again and catch such a left over task.
*/
if (!error) {
pr_info("Double checking all user space processes after OOM killer disable... ");
error = try_to_freeze_tasks(true);
pr_cont("\n");
}
if (error) if (error)
thaw_processes(); thaw_processes();
return error; return error;