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Subject: Re: WARNING in try_charge
To:     Michal Hocko <mhocko@kernel.org>,
        syzbot <syzbot+bab151e82a4e973fa325@syzkaller.appspotmail.com>
Cc:     cgroups@vger.kernel.org, dvyukov@google.com, hannes@cmpxchg.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        syzkaller-bugs@googlegroups.com, vdavydov.dev@gmail.com,
        David Howells <dhowells@redhat.com>
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 <00000000000070698b0572c28ebc@google.com>
 <20180806113212.GK19540@dhcp22.suse.cz>
From:   Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
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Date:   Mon, 6 Aug 2018 23:41:22 +0900
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+David Howells

On 2018/08/06 20:32, Michal Hocko wrote:
> On Mon 06-08-18 04:27:02, syzbot wrote:
>> Hello,
>>
>> syzbot has tested the proposed patch and the reproducer did not trigger
>> crash:
>>
>> Reported-and-tested-by:
>> syzbot+bab151e82a4e973fa325@syzkaller.appspotmail.com
>>
>> Tested on:
>>
>> commit:         8c8399e0a3fb Add linux-next specific files for 20180806
>> git tree:       linux-next
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=1b6bc1781e49e93e
>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>> patch:          https://syzkaller.appspot.com/x/patch.diff?x=14fe18e2400000
>>
>> Note: testing is done by a robot and is best-effort only.
> 
> OK, so this smells like a problem in the previous group oom changes. Or
> maybe it is not very easy to reproduce?
> 

Since I can't find mm related changes between next-20180803 (syzbot can reproduce) and
next-20180806 (syzbot has not reproduced), I can't guess what makes this problem go away.

But since this problem did not occur for 3.5 hours on next-20180806 (when this problem
was occurring once per 60-90 minutes), the reproducer might not be working as intended
due to "kernfs, sysfs, cgroup, intel_rdt: Support fs_context" or something...

  ./kernel/cgroup/cgroup-internal.h                                          |    3
  ./kernel/cgroup/cgroup-v1.c                                                |  211
  ./kernel/cgroup/cgroup.c                                                   |   81