linux-kernel - Re: WARNING in try

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Date:   Mon, 6 Aug 2018 13:09:34 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+bab151e82a4e973fa325@...kaller.appspotmail.com>,
        cgroups@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>
Subject: Re: WARNING in try_charge

On Mon 06-08-18 19:47:00, Tetsuo Handa wrote:
> On 2018/08/06 19:39, Dmitry Vyukov wrote:
> > On Mon, Aug 6, 2018 at 11:48 AM, Michal Hocko <mhocko@...nel.org> wrote:
> >> Btw. running with the above diff on top might help us to ideantify
> >> whether this is a pre-mature warning or a valid one. Still useful to
> >> find out.
> 
> Since syzbot already found a syz reproducer, you can ask syzbot to test it.
> 
> > 
> > The bug report has a reproducer, so you can run it with the patch. Or
> > ask syzbot to test your patch:
> > https://github.com/google/syzkaller/blob/master/docs/syzbot.md#testing-patches
> > Which basically boils down to saying:
> > 
> > #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > master
> 
> Excuse me, but this is linux-next only problem. Therefore,

If this really is a linux-next only problem then please retest with the
current linux-next which has dropped the and replaced the group oom
code.

> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 4603ad75c9a9..852cd3dbdcd9 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1388,6 +1388,8 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  	bool ret;
>  
>  	mutex_lock(&oom_lock);
> +	pr_info("task=%s pid=%d invoked memcg oom killer. oom_victim=%d\n",
> +			current->comm, current->pid, tsk_is_oom_victim(current));
>  	ret = out_of_memory(&oc);
>  	mutex_unlock(&oom_lock);
>  	return ret;
> 
> F.Y.I. Waiting until __mmput() completes (with timeout using OOM score feedback)
> ( https://syzkaller.appspot.com/x/patch.diff?x=101e449c400000 ) solves this race.

Which just means that something else is broken. Seriously, timout is not
going to fix anything. It merely changes the picture.

-- 
Michal Hocko
SUSE Labs