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

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Date:   Wed, 18 Jul 2018 15:04:40 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Eric Van Hensbergen <ericvh@...il.com>,
        Ron Minnich <rminnich@...dia.gov>,
        Latchesar Ionkov <lucho@...kov.net>,
        v9fs-developer@...ts.sourceforge.net,
        syzbot <syzbot+f425456ea8aa16b40d20@...kaller.appspotmail.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: INFO: task hung in grab_super

On Wed, Jul 18, 2018 at 2:53 PM, Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
> On 2018/07/18 20:41, Dmitry Vyukov wrote:
>> This seems to be related to 9p. After rerunning the log I got:
>>
>> root@...kaller:~# ps afxu | grep syz
>> root     18253  0.0  0.0      0     0 ttyS0    Zl   10:16   0:00  \_
>> [syz-executor] <defunct>
>> root@...kaller:~# cat /proc/18253/task/*/stack
>> [<0>] p9_client_rpc+0x3a2/0x1400
>> [<0>] p9_client_flush+0x134/0x2a0
>> [<0>] p9_client_rpc+0x122c/0x1400
>> [<0>] p9_client_create+0xc56/0x16af
>> [<0>] v9fs_session_init+0x21a/0x1a80
>> [<0>] v9fs_mount+0x7c/0x900
>> [<0>] mount_fs+0xae/0x328
>> [<0>] vfs_kern_mount.part.34+0xdc/0x4e0
>> [<0>] do_mount+0x581/0x30e0
>> [<0>] ksys_mount+0x12d/0x140
>> [<0>] __x64_sys_mount+0xbe/0x150
>> [<0>] do_syscall_64+0x1b9/0x820
>> [<0>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> [<0>] 0xffffffffffffffff
>>
>> There is a bunch of hangs in 9p, so let's do:
>>
>> #syz dup: INFO: task hung in flush_work
>>
> Then, is dumping all threads when khungtaskd fires a candidate
> for CONFIG_DEBUG_AID_FOR_SYZBOT=y path?

Perhaps would be useful. But maybe only tasks that are blocked for
more than timeout/2? and/or unkillable tasks? killable tasks are not a
problem.

Btw, I see that p9_client_rpc uses wait_event_killable, why wasn't it
killed along with the whole process?