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

From: Rong Chen <rong.a.chen@intel.com>
To: Michal Hocko <mhocko@kernel.org>, kbuild test robot <lkp@intel.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org, kbuild-all@01.org,
	Johannes Weiner <hannes@cmpxchg.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [kbuild-all] [PATCH 2/2] memcg: do not report racy no-eligible OOM tasks
Date: Fri, 11 Jan 2019 08:23:57 +0800	[thread overview]
Message-ID: <a0312c1e-dfed-5cff-c660-e1c1bea9843b@intel.com> (raw)
In-Reply-To: <20190108093959.GQ31793@dhcp22.suse.cz>

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  	}