From: Dmitry Vyukov <dvyukov@google.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: syzbot
<bot+e38be687a2450270a3b593bacb6b5795a7a74edb@syzkaller.appspotmail.com>,
syzkaller-bugs@googlegroups.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Kate Stewart <kstewart@linuxfoundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Philippe Ombredanne <pombredanne@nexb.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: BUG: workqueue lockup (2)
Date: Tue, 19 Dec 2017 17:37:48 +0100 [thread overview]
Message-ID: <CACT4Y+YZ6yuZqrjAxHEadW56TVS=x=WQqrfRrvMQ=LHU3+Kd8A@mail.gmail.com> (raw)
In-Reply-To: <CACT4Y+ZbE5=yeb=3hL8KDpPLarHJgihsTb6xX2+4fnoLFuBTow@mail.gmail.com>
On Tue, Dec 19, 2017 at 3:40 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Tue, Dec 19, 2017 at 3:27 PM, Tetsuo Handa
> <penguin-kernel@i-love.sakura.ne.jp> wrote:
>> syzbot wrote:
>>>
>>> syzkaller has found reproducer for the following crash on
>>> f3b5ad89de16f5d42e8ad36fbdf85f705c1ae051
>>
>> "BUG: workqueue lockup" is not a crash.
>
> Hi Tetsuo,
>
> What is the proper name for all of these collectively?
>
>
>>> 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
>>
>> You gave up too early. There is no hint for understanding what was going on.
>> While we can observe "BUG: workqueue lockup" under memory pressure, there is
>> no hint like SysRq-t and SysRq-m. Thus, I can't tell something is wrong.
>
> Do you know how to send them programmatically? I tried to find a way
> several times, but failed. Articles that I've found talk about
> pressing some keys that don't translate directly to us-ascii.
On second though, some oopses automatically dump locks/tasks. Should
we do the same for this oops?
> But you can also run the reproducer. No report can possible provide
> all possible useful information, sometimes debugging boils down to
> manually adding printfs. That's why syzbot aims at providing a
> reproducer as the ultimate source of details. Also since a developer
> needs to test a proposed fix, it's easier to start with the reproducer
> right away.
>
>
>> At least you need to confirm that lockup lasts for a few minutes. Otherwise,
>
> Is it possible to increase the timeout? How? We could bump it up to 2 minutes.
>
>
>> this might be just overstressing. (According to repro.c , 12 threads are
>> created and soon SEGV follows? According to above message, only 2 CPUs?
>> Triggering SEGV suggests memory was low due to saving coredump?)
next prev parent reply other threads:[~2017-12-19 16:38 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <94eb2c03c9bc75aff2055f70734c@google.com>
2017-12-03 14:36 ` BUG: workqueue lockup (2) Dmitry Vyukov
2017-12-03 14:48 ` Thomas Gleixner
2017-12-04 11:08 ` Tetsuo Handa
2017-12-19 12:25 ` syzbot
2017-12-19 14:27 ` Tetsuo Handa
2017-12-19 14:40 ` Dmitry Vyukov
2017-12-19 16:37 ` Dmitry Vyukov [this message]
2017-12-20 10:55 ` Tetsuo Handa
2017-12-21 10:19 ` Dmitry Vyukov
2017-12-21 10:22 ` Dmitry Vyukov
2017-12-21 11:04 ` Dmitry Vyukov
2017-12-21 13:07 ` Tetsuo Handa
2017-12-28 13:43 ` Dmitry Vyukov
2018-05-12 21:52 ` Eric Biggers
2018-05-13 2:06 ` Tetsuo Handa
2018-05-13 3:32 ` Eric Biggers
2018-05-13 14:29 ` Tetsuo Handa
2018-05-13 14:35 ` Dmitry Vyukov
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