linux-kernel - Re: INFO: rcu detected stall in sys

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Message-ID: <1737a5e1-f93a-e7ea-80d0-c244b22d0b61@I-love.SAKURA.ne.jp>
Date:   Sat, 19 Jan 2019 22:00:55 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+1505c80c74256c6118a5@...kaller.appspotmail.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Amir Goldstein <amir73il@...il.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dave Chinner <david@...morbit.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hugh Dickins <hughd@...gle.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: INFO: rcu detected stall in sys_sendfile64 (2)

On 2019/01/19 20:41, Dmitry Vyukov wrote:
> On Sat, Jan 19, 2019 at 12:32 PM syzbot
> <syzbot+1505c80c74256c6118a5@...kaller.appspotmail.com> wrote:
>>
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit:    2339e91d0e66 Merge tag 'media/v5.0-1' of git://git.kernel...
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=175f2638c00000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=abc3dc9b7a900258
>> dashboard link: https://syzkaller.appspot.com/bug?extid=1505c80c74256c6118a5
>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12c4dc28c00000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15df4108c00000
> 
> Looking at the reproducer it looks like something with scheduler as it
> involves perf_event_open and sched_setattr. So +Peter and Mingo.
> Is it the same root cause as the other stalls involving sched_setattr?

Yes. I think sched_setattr() involves this problem.

Reproducers from "BUG: workqueue lockup (4)" at
https://syzkaller.appspot.com/text?tag=ReproC&x=13ec31a5400000
involves sched_setattr(SCHED_DEADLINE) and
https://syzkaller.appspot.com/text?tag=ReproC&x=104da690c00000
also involves sched_setattr().