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authorMichal Hocko <mhocko@suse.com>2016-03-25 14:20:41 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-03-25 16:37:42 -0700
commite26796066fdf929cbba22dabb801808f986acdb9 (patch)
treeef8564918c72f9c8e79269077e723ac76a69dc73
parent29c696e1c6eceb5db6b21f0c89495fcfcd40c0eb (diff)
oom: make oom_reaper freezable
After "oom: clear TIF_MEMDIE after oom_reaper managed to unmap the address space" oom_reaper will call exit_oom_victim on the target task after it is done. This might however race with the PM freezer: CPU0 CPU1 CPU2 freeze_processes try_to_freeze_tasks # Allocation request out_of_memory oom_killer_disable wake_oom_reaper(P1) __oom_reap_task exit_oom_victim(P1) wait_event(oom_victims==0) [...] do_exit(P1) perform IO/interfere with the freezer which breaks the oom_killer_disable semantic. We no longer have a guarantee that the oom victim won't interfere with the freezer because it might be anywhere on the way to do_exit while the freezer thinks the task has already terminated. It might trigger IO or touch devices which are frozen already. In order to close this race, make the oom_reaper thread freezable. This will work because a) already running oom_reaper will block freezer to enter the quiescent state b) wake_oom_reaper will not wake up the reaper after it has been frozen c) the only way to call exit_oom_victim after try_to_freeze_tasks is from the oom victim's context when we know the further interference shouldn't be possible Signed-off-by: Michal Hocko <mhocko@suse.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: David Rientjes <rientjes@google.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/oom_kill.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index a49638f41e45..8cc55f0f0e5c 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -525,6 +525,8 @@ static void oom_reap_task(struct task_struct *tsk)
static int oom_reaper(void *unused)
{
+ set_freezable();
+
while (true) {
struct task_struct *tsk = NULL;

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