Re: [PATCH v2] mm,oom: don't abort on exiting processes when selecting a victim.
From: Michal Hocko <mhocko@kernel.org>
Date: 2016-02-17 14:39:21
Also in:
lkml
On Wed 17-02-16 23:31:25, Tetsuo Handa wrote:
Currently, oom_scan_process_thread() returns OOM_SCAN_ABORT when there is
a thread which is exiting. But it is possible that that thread is blocked
at down_read(&mm->mmap_sem) in exit_mm() called from do_exit() whereas
one of threads sharing that memory is doing a GFP_KERNEL allocation
between down_write(&mm->mmap_sem) and up_write(&mm->mmap_sem)
(e.g. mmap()).
----------
T1 T2
Calls mmap()
Calls _exit(0)
Arrives at vm_mmap_pgoff()
Arrives at do_exit()
Gets PF_EXITING via exit_signals()
Calls down_write(&mm->mmap_sem)
Calls do_mmap_pgoff()
Calls down_read(&mm->mmap_sem) from exit_mm()
Calls out of memory via a GFP_KERNEL allocation but
oom_scan_process_thread(T1) returns OOM_SCAN_ABORT
----------
down_read(&mm->mmap_sem) by T1 is waiting for up_write(&mm->mmap_sem) by
T2 while oom_scan_process_thread() by T2 is waiting for T1 to set
T1->mm = NULL. Under such situation, the OOM killer does not choose
a victim, which results in silent OOM livelock problem.
This patch changes oom_scan_process_thread() not to return OOM_SCAN_ABORT
when there is a thread which is exiting.Thank you for the updated changelog. This makes much more sense now. This problem exists for quite some time but I would be hesitant to mark it for stable because the side effects are quite hard to evaluate. We could e.g. see a premature OOM killer invocation while the currently exiting task just didn't get to finish and release its mm.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
quoted hunk ↗ jump to hunk
--- mm/oom_kill.c | 3 --- 1 file changed, 3 deletions(-)diff --git a/mm/oom_kill.c b/mm/oom_kill.c index cf87153..6e6abaf 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c@@ -292,9 +292,6 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc, if (oom_task_origin(task)) return OOM_SCAN_SELECT; - if (task_will_free_mem(task) && !is_sysrq_oom(oc)) - return OOM_SCAN_ABORT; - return OOM_SCAN_OK; }-- 1.8.3.1
-- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>