linux-kernel - Re: BUG: workqueue lockup (2)

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Date:   Sat, 12 May 2018 14:52:22 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     syzbot 
        <bot+e38be687a2450270a3b593bacb6b5795a7a74edb@...kaller.appspotmail.com>
Cc:     dvyukov@...gle.com, gregkh@...uxfoundation.org,
        kstewart@...uxfoundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, penguin-kernel@...ove.SAKURA.ne.jp,
        pombredanne@...b.com, syzkaller-bugs@...glegroups.com,
        tglx@...utronix.de
Subject: Re: BUG: workqueue lockup (2)

On Tue, Dec 19, 2017 at 04:25:01AM -0800, syzbot wrote:
> syzkaller has found reproducer for the following crash on
> f3b5ad89de16f5d42e8ad36fbdf85f705c1ae051
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> C reproducer is attached
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers
> 
> 
> BUG: workqueue lockup - pool cpus=1 node=0 flags=0x0 nice=0 stuck for 37s!
> BUG: workqueue lockup - pool cpus=1 node=0 flags=0x0 nice=-20 stuck for 32s!
> Showing busy workqueues and worker pools:
> workqueue events: flags=0x0
>   pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/256
>     pending: cache_reap
> workqueue events_power_efficient: flags=0x80
>   pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=2/256
>     pending: neigh_periodic_work, do_cache_clean
> workqueue mm_percpu_wq: flags=0x8
>   pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=1/256
>     pending: vmstat_update
> workqueue kblockd: flags=0x18
>   pwq 3: cpus=1 node=0 flags=0x0 nice=-20 active=1/256
>     pending: blk_timeout_work
> 

The bug that this reproducer reproduces was fixed a while ago by commit
966031f340185e, so I'm marking this bug report fixed by it:

#syz fix: n_tty: fix EXTPROC vs ICANON interaction with TIOCINQ (aka FIONREAD)

Note that the error message was not always "BUG: workqueue lockup"; it was also
sometimes like "watchdog: BUG: soft lockup - CPU#5 stuck for 22s!".

syzbot still is hitting the "BUG: workqueue lockup" error sometimes, but it must
be for other reasons.  None has a reproducer currently.

- Eric