From: Dmitry Vyukov <dvyukov@google.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: David Rientjes <rientjes@google.com>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
syzbot <syzbot+77e6b28a7a7106ad0def@syzkaller.appspotmail.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Andrew Morton <akpm@linux-foundation.org>,
guro@fb.com,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Yang Shi <yang.s@alibaba-inc.com>
Subject: Re: INFO: rcu detected stall in shmem_fault
Date: Wed, 10 Oct 2018 11:33:14 +0200 [thread overview]
Message-ID: <CACT4Y+Y1AAw3M7_weNDZ5eb5ON_bj-sYFHNJmQa0i4uKEy4W5Q@mail.gmail.com> (raw)
In-Reply-To: <20181010091309.GE5873@dhcp22.suse.cz>
On Wed, Oct 10, 2018 at 11:13 AM, Michal Hocko <mhocko@kernel.org> wrote:
> On Wed 10-10-18 09:55:57, Dmitry Vyukov wrote:
>> On Wed, Oct 10, 2018 at 6:11 AM, 'David Rientjes' via syzkaller-bugs
>> <syzkaller-bugs@googlegroups.com> wrote:
>> > On Wed, 10 Oct 2018, Tetsuo Handa wrote:
>> >
>> >> syzbot is hitting RCU stall due to memcg-OOM event.
>> >> https://syzkaller.appspot.com/bug?id=4ae3fff7fcf4c33a47c1192d2d62d2e03efffa64
>> >>
>> >> What should we do if memcg-OOM found no killable task because the allocating task
>> >> was oom_score_adj == -1000 ? Flooding printk() until RCU stall watchdog fires
>> >> (which seems to be caused by commit 3100dab2aa09dc6e ("mm: memcontrol: print proper
>> >> OOM header when no eligible victim left") because syzbot was terminating the test
>> >> upon WARN(1) removed by that commit) is not a good behavior.
>>
>>
>> You want to say that most of the recent hangs and stalls are actually
>> caused by our attempt to sandbox test processes with memory cgroup?
>> The process with oom_score_adj == -1000 is not supposed to consume any
>> significant memory; we have another (test) process with oom_score_adj
>> == 0 that's actually consuming memory.
>> But should we refrain from using -1000? Perhaps it would be better to
>> use -500/500 for control/test process, or -999/1000?
>
> oom disable on a task (especially when this is the only task in the
> memcg) is tricky. Look at the memcg report
> [ 935.562389] Memory limit reached of cgroup /syz0
> [ 935.567398] memory: usage 204808kB, limit 204800kB, failcnt 6081
> [ 935.573768] memory+swap: usage 0kB, limit 9007199254740988kB, failcnt 0
> [ 935.580650] kmem: usage 0kB, limit 9007199254740988kB, failcnt 0
> [ 935.586923] Memory cgroup stats for /syz0: cache:152KB rss:176336KB rss_huge:163840KB shmem:344KB mapped_file:264KB dirty:0KB writeback:0KB swap:0KB inactive_anon:260KB active_anon:176448KB inactive_file:4KB active_file:0KB
>
> There is still somebody holding anonymous (THP) memory. If there is no
> other eligible oom victim then it must be some of the oom disabled ones.
> You have suppressed the task list information so we do not know who that
> might be though.
>
> So it looks like there is some misconfiguration or a bug in the oom
> victim selection.
I afraid KASAN can interfere with memory accounting/OMM killing too.
KASAN quarantines up to 1/32-th of physical memory (in our case
7.5GB/32 = 230MB) that is already freed by the task, but as far as I
understand is still accounted against memcg. So maybe making cgroup
limit >> quarantine size will help to resolve this too.
But of course there can be a plain memory leak too.
next prev parent reply other threads:[~2018-10-10 9:33 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-10 0:08 INFO: rcu detected stall in shmem_fault syzbot
2018-10-10 0:12 ` Tetsuo Handa
2018-10-10 4:11 ` David Rientjes
2018-10-10 7:55 ` Dmitry Vyukov
2018-10-10 9:13 ` Michal Hocko
2018-10-10 9:33 ` Dmitry Vyukov [this message]
2018-10-10 9:02 ` Michal Hocko
2018-10-10 8:59 ` Michal Hocko
2018-10-10 10:43 ` Tetsuo Handa
2018-10-10 11:35 ` Michal Hocko
2018-10-10 11:48 ` Sergey Senozhatsky
2018-10-10 12:25 ` Michal Hocko
2018-10-10 12:29 ` Dmitry Vyukov
2018-10-10 12:36 ` Dmitry Vyukov
2018-10-10 13:10 ` Tetsuo Handa
2018-10-10 13:17 ` Dmitry Vyukov
2018-10-11 1:17 ` Sergey Senozhatsky
2018-10-10 15:17 ` Sergey Senozhatsky
2018-10-10 14:19 ` Tetsuo Handa
2018-10-10 15:11 ` [RFC PATCH] memcg, oom: throttle dump_header for memcg ooms without eligible tasks Michal Hocko
2018-10-11 6:37 ` Tetsuo Handa
2018-10-12 10:47 ` Tetsuo Handa
2018-10-12 11:20 ` Johannes Weiner
2018-10-12 12:08 ` Michal Hocko
2018-10-12 12:10 ` Tetsuo Handa
2018-10-12 12:41 ` Johannes Weiner
2018-10-12 12:58 ` Tetsuo Handa
2018-10-13 11:09 ` Tetsuo Handa
2018-10-13 11:22 ` Johannes Weiner
2018-10-13 11:28 ` Tetsuo Handa
2018-10-15 8:19 ` Michal Hocko
2018-10-15 10:57 ` Tetsuo Handa
2018-10-15 11:24 ` Michal Hocko
2018-10-15 12:47 ` Tetsuo Handa
2018-10-15 13:35 ` Michal Hocko
2018-10-16 0:55 ` Tetsuo Handa
2018-10-16 9:20 ` Michal Hocko
2018-10-16 11:05 ` Tetsuo Handa
2018-10-16 11:17 ` Michal Hocko
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