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.
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
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
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