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

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Date:   Mon, 5 Nov 2018 11:40:40 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+6339eda9cb4ebbc4c37b@...kaller.appspotmail.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: INFO: task hung in fuse_sb_destroy

On Thu, Nov 1, 2018 at 12:05 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Thu, Nov 1, 2018 at 11:49 AM, syzbot
> <syzbot+6339eda9cb4ebbc4c37b@...kaller.appspotmail.com> wrote:
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit:    59fc453b21f7 Merge branch 'akpm' (patches from Andrew)
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=15fb2447400000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=ea045471e4c756e8
>> dashboard link: https://syzkaller.appspot.com/bug?extid=6339eda9cb4ebbc4c37b
>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=178a105d400000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16651133400000
>
>
> I can easily reproduce this.

I can't reproduce on my meager dual core notebook.

>
> The repro gives me a task hanged at:
>
> # cat /proc/7563/task/*/stack
> [<0>] fuse_wait_aborted+0x20b/0x320
> [<0>] fuse_sb_destroy+0xe2/0x1d0
> [<0>] fuse_kill_sb_anon+0x15/0x20
> [<0>] deactivate_locked_super+0x97/0x100
> [<0>] deactivate_super+0x2bb/0x320
> [<0>] cleanup_mnt+0xbf/0x160
> [<0>] __cleanup_mnt+0x16/0x20
> [<0>] task_work_run+0x1e8/0x2a0
> [<0>] exit_to_usermode_loop+0x318/0x380
> [<0>] do_syscall_64+0x6be/0x820
> [<0>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [<0>] 0xffffffffffffffff
>
> I double checked that writing to /sys/fs/fuse/connections/44/abort did
> not help (the only entry in fuse/connections). Wrote multiple times,
> and tried to kill the task, nothing helps.

What's the output of

cat /sys/fs/fuse/connections/NN/waiting

?

Thanks,
Miklos