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

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Message-ID: <CACT4Y+YqWgZZFXdX2A2jVYEdHfY9ywGMgRRP5W4Uqdu__rA63g@mail.gmail.com>
Date:   Wed, 19 Dec 2018 19:42:17 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     syzbot <syzbot+bcad772bbc241b4c6147@...kaller.appspotmail.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        James Morris <jmorris@...ei.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org,
        "Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: INFO: rcu detected stall in sys_sendfile64

On Wed, Dec 19, 2018 at 11:13 AM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> On 2018/12/19 18:27, syzbot wrote:
> > HEAD commit:    ddfbab46539f Merge tag 'scsi-fixes' of git://git.kernel.or..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=15b87fa3400000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=861a3573f4e78ba1
> > dashboard link: https://syzkaller.appspot.com/bug?extid=bcad772bbc241b4c6147
> > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13912ccd400000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=145781db400000
>
> This is not a LSM problem, for the reproducer is calling
> sched_setattr(SCHED_DEADLINE) with very large values.
>
>   sched_setattr(0, {size=0, sched_policy=0x6 /* SCHED_??? */, sched_flags=0, sched_nice=0, sched_priority=0, sched_runtime=2251799813724439, sched_deadline=4611686018427453437, sched_period=0}, 0) = 0
>
> I think that this problem is nothing but an insane sched_setattr() parameter.
>
> #syz invalid

Note there was another one with sched_setattr, which turned out to be
some serious problem in kernel (sched_setattr should not cause CPU
stall for 3 minutes):
INFO: rcu detected stall in do_idle
https://syzkaller.appspot.com/bug?extid=385468161961cee80c31
https://groups.google.com/forum/#!msg/syzkaller-bugs/crrfvusGtwI/IoD_zus4BgAJ

Maybe it another incarnation of the same bug, that one is still not fixed.