Re: [PATCH] mm,oom_reaper: Check for MMF_OOM_SKIP before complain.

From: Michal Hocko <mhocko@suse.com>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: akpm@linux-foundation.org, rientjes@google.com, linux-mm@kvack.org
Subject: Re: [PATCH] mm,oom_reaper: Check for MMF_OOM_SKIP before complain.
Date: Thu, 22 Mar 2018 12:59:43 +0100	[thread overview]
Message-ID: <20180322115943.GE23100@dhcp22.suse.cz> (raw)
In-Reply-To: <201803221946.DHG65638.VFJHFtOSQLOMOF@I-love.SAKURA.ne.jp>

On Thu 22-03-18 19:46:36, Tetsuo Handa wrote:
> >From b141cdbe0db852549c94d5b1e6a9967ca69d59fd Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Thu, 22 Mar 2018 19:44:12 +0900
> Subject: [PATCH] mm,oom_reaper: Check for MMF_OOM_SKIP before complain.
> 
> I got "oom_reaper: unable to reap pid:" messages when the victim thread
> was blocked inside free_pgtables() (which occurred after returning from
> unmap_vmas() and setting MMF_OOM_SKIP). We don't need to complain when
> exit_mmap() already set MMF_OOM_SKIP.

... because we do not report a failure when MMF_OOM_SKIP is set already
(see __oom_reap_task_mm).

> [  663.593821] Killed process 7558 (a.out) total-vm:4176kB, anon-rss:84kB, file-rss:0kB, shmem-rss:0kB
> [  664.684801] oom_reaper: unable to reap pid:7558 (a.out)
> [  664.892292] a.out           D13272  7558   6931 0x00100084
> [  664.895765] Call Trace:
> [  664.897574]  ? __schedule+0x25f/0x780
> [  664.900099]  schedule+0x2d/0x80
> [  664.902260]  rwsem_down_write_failed+0x2bb/0x440
> [  664.905249]  ? rwsem_down_write_failed+0x55/0x440
> [  664.908335]  ? free_pgd_range+0x569/0x5e0
> [  664.911145]  call_rwsem_down_write_failed+0x13/0x20
> [  664.914121]  down_write+0x49/0x60
> [  664.916519]  ? unlink_file_vma+0x28/0x50
> [  664.919255]  unlink_file_vma+0x28/0x50
> [  664.922234]  free_pgtables+0x36/0x100
> [  664.924797]  exit_mmap+0xbb/0x180
> [  664.927220]  mmput+0x50/0x110
> [  664.929504]  copy_process.part.41+0xb61/0x1fe0
> [  664.932448]  ? _do_fork+0xe6/0x560
> [  664.934902]  ? _do_fork+0xe6/0x560
> [  664.937361]  _do_fork+0xe6/0x560
> [  664.939742]  ? syscall_trace_enter+0x1a9/0x240
> [  664.942693]  ? retint_user+0x18/0x18
> [  664.945309]  ? page_fault+0x2f/0x50
> [  664.947896]  ? trace_hardirqs_on_caller+0x11f/0x1b0
> [  664.951075]  do_syscall_64+0x74/0x230
> [  664.953747]  entry_SYSCALL_64_after_hwframe+0x42/0xb7
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Acked-by: David Rientjes <rientjes@google.com>
> Cc: Michal Hocko <mhocko@suse.com>

OK, fair enough. I think it is on borderline of usefulness but it
doesn't seem harmful. I can already see somebody asking why the
MMF_OOM_SKIP really requires mmap_sem in __oom_reap_task_mm while it
doesn't in oom_reap_task but what ever. 

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/oom_kill.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 5336985..dfd3705 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -590,7 +590,8 @@ static void oom_reap_task(struct task_struct *tsk)
>  	while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm))
>  		schedule_timeout_idle(HZ/10);
>  
> -	if (attempts <= MAX_OOM_REAP_RETRIES)
> +	if (attempts <= MAX_OOM_REAP_RETRIES ||
> +	    test_bit(MMF_OOM_SKIP, &mm->flags))
>  		goto done;
>  
>  
> -- 
> 1.8.3.1

-- 
Michal Hocko
SUSE Labs