Re: [PATCH] mm: fix oom work when memory is under pressure

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Tetsuo Handa wrote:
> As of 4.8-rc6, the OOM reaper cannot take mmap_sem for read at __oom_reap_task()
> because of TIF_MEMDIE thread waiting at ksm_exit() from __mmput() from mmput()
>  from exit_mm() from do_exit(). Thus, __oom_reap_task() returns false and
> oom_reap_task() will emit "oom_reaper: unable to reap pid:%d (%s)\n" message.
> Then, oom_reap_task() clears TIF_MEMDIE from that thread, which in turn
> makes oom_scan_process_thread() not to return OOM_SCAN_ABORT because
> atomic_read(&task->signal->oom_victims) becomes 0 due to exit_oom_victim()
> by the OOM reaper. Then, the OOM killer selects next OOM victim because
> ksmd is waking up the OOM killer via a __GFP_FS allocation request.

Oops. As of 4.8-rc6, __oom_reap_task() returns true because of
find_lock_task_mm() returning NULL. Thus, oom_reap_task() clears TIF_MEMDIE
without emitting "oom_reaper: unable to reap pid:%d (%s)\n" message.

> 
> Thus, this bug will be completely solved (at the cost of selecting next
> OOM victim) as of 4.8-rc6.

The conclusion is same.

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