linux-kernel - Re: INFO: task hung in fsnotify_mark_destroy

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Date:   Thu, 19 Apr 2018 17:42:17 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Jan Kara <jack@...e.cz>
Cc:     syzbot <syzbot+e38306788a2e7102a3b6@...kaller.appspotmail.com>,
        amir73il@...il.com, Dan Carpenter <dan.carpenter@...cle.com>,
        David Windsor <dwindsor@...il.com>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, mszeredi@...hat.com,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>
Subject: Re: INFO: task hung in fsnotify_mark_destroy_workfn

On Wed, Apr 18, 2018 at 11:36 AM, Jan Kara <jack@...e.cz> wrote:
> Hello,
>
> On Tue 17-04-18 18:02:02, syzbot wrote:
>> syzbot hit the following crash on upstream commit
>> a27fc14219f2e3c4a46ba9177b04d9b52c875532 (Mon Apr 16 21:07:39 2018 +0000)
>> Merge branch 'parisc-4.17-3' of
>> git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux
>> syzbot dashboard link:
>> https://syzkaller.appspot.com/bug?extid=e38306788a2e7102a3b6
>>
>> syzkaller reproducer:
>> https://syzkaller.appspot.com/x/repro.syz?id=5126465372815360
>> Raw console output:
>> https://syzkaller.appspot.com/x/log.txt?id=5956756370882560
>> Kernel config:
>> https://syzkaller.appspot.com/x/.config?id=-5914490758943236750
>> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+e38306788a2e7102a3b6@...kaller.appspotmail.com
>> It will help syzbot understand when the bug is fixed. See footer for
>> details.
>> If you forward the report, please keep this part and the footer.
>>
>
> Removed binder messages from the lockup splat so that it's more readable.


These messages seems to be relevant and likely the root cause of the hang.
+binder maintainers


>> INFO: task kworker/u4:4:853 blocked for more than 120 seconds.
>>       Not tainted 4.17.0-rc1+ #6
>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> kworker/u4:4    D11512   853      2 0x80000000
>> Workqueue: events_unbound fsnotify_mark_destroy_workfn
>> Call Trace:
>>  context_switch kernel/sched/core.c:2848 [inline]
>>  __schedule+0x801/0x1e30 kernel/sched/core.c:3490
>>  schedule+0xef/0x430 kernel/sched/core.c:3549
>>  schedule_timeout+0x1b5/0x240 kernel/time/timer.c:1777
>>  do_wait_for_common kernel/sched/completion.c:83 [inline]
>>  __wait_for_common kernel/sched/completion.c:104 [inline]
>>  wait_for_common kernel/sched/completion.c:115 [inline]
>>  wait_for_completion+0x3e7/0x870 kernel/sched/completion.c:136
>>  __synchronize_srcu+0x189/0x240 kernel/rcu/srcutree.c:924
>>  synchronize_srcu+0x408/0x54f kernel/rcu/srcutree.c:1002
>>  fsnotify_mark_destroy_workfn+0x1aa/0x530 fs/notify/mark.c:759
>>  process_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
>>  worker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
>>  kthread+0x345/0x410 kernel/kthread.c:238
>>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
>
> OK, so we are waiting for the grace period on fsnotify_mark_srcu. Seems
> like someone is holding fsnotify_mark_srcu too long or srcu period cannot
> finish for some other reason. However the reproducer basically contains
> only one binder ioctl and I have no idea how that's connected with fsnotify
> in any way. So either the reproducer is wrong, or binder is corrupting
> memory and fsnotify is just a victim, or something like that...
>
>                                                                 Honza
> --
> Jan Kara <jack@...e.com>
> SUSE Labs, CR
>
> --
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