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

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Date:   Fri, 11 Jan 2019 08:23:57 +0800
From:   Rong Chen <rong.a.chen@...el.com>
To:     Michal Hocko <mhocko@...nel.org>, kbuild test robot <lkp@...el.com>
Cc:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        kbuild-all@...org, Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [kbuild-all] [PATCH 2/2] memcg: do not report racy no-eligible
 OOM tasks



On 01/08/2019 05:39 PM, Michal Hocko wrote:
> 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?

Thanks for your reply. It looks like a false positive. We'll look into it.

Best Regards,
Rong Chen

>
> [...]
>> 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  	}