linux-kernel - Re: [PATCH 2/2] memcg: do not report racy no-eligible OOM tasks

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Message-ID: <20190108093959.GQ31793@dhcp22.suse.cz>
Date:   Tue, 8 Jan 2019 10:39:59 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     kbuild test robot <lkp@...el.com>
Cc:     kbuild-all@...org, linux-mm@...ck.org,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] memcg: do not report racy no-eligible OOM tasks

On Tue 08-01-19 16:35:42, kbuild test robot wrote:
[...]
> All warnings (new ones prefixed by >>):
> 
>    include/linux/rcupdate.h:659:9: warning: context imbalance in 'find_lock_task_mm' - wrong count at exit
>    include/linux/sched/mm.h:141:37: warning: dereference of noderef expression
>    mm/oom_kill.c:225:28: warning: context imbalance in 'oom_badness' - unexpected unlock
>    mm/oom_kill.c:406:9: warning: context imbalance in 'dump_tasks' - different lock contexts for basic block
> >> mm/oom_kill.c:918:17: warning: context imbalance in '__oom_kill_process' - unexpected unlock

What exactly does this warning say? I do not see anything wrong about
the code. find_lock_task_mm returns a locked task when t != NULL and
mark_oom_victim doesn't do anything about the locking. Am I missing
something or the warning is just confused?

[...]
> 00508538 Michal Hocko          2019-01-07  915  		t = find_lock_task_mm(p);
> 00508538 Michal Hocko          2019-01-07  916  		if (!t)
> 00508538 Michal Hocko          2019-01-07  917  			continue;
> 00508538 Michal Hocko          2019-01-07 @918  		mark_oom_victim(t);
> 00508538 Michal Hocko          2019-01-07  919  		task_unlock(t);
> 647f2bdf David Rientjes        2012-03-21  920  	}

-- 
Michal Hocko
SUSE Labs