From: Jens Axboe <axboe@kernel.dk>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>,
syzbot+c0cf869505e03bdf1a24@syzkaller.appspotmail.com,
christophe.jaillet@wanadoo.fr,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
syzkaller-bugs@googlegroups.com, zhangweiping@didichuxing.com,
Andrew Morton <akpm@linux-foundation.org>,
Dmitry Vyukov <dvyukov@google.com>,
linux-block <linux-block@vger.kernel.org>
Subject: Re: INFO: task hung in wb_shutdown (2)
Date: Tue, 1 May 2018 15:30:59 -0600 [thread overview]
Message-ID: <bd3e8460-9794-6b57-e7d6-7e18ea34ac0c@kernel.dk> (raw)
In-Reply-To: <CA+55aFxaa_+uZ=bOVdevcUwG7ncue7O+i06q4Kb=bWACGwCBjQ@mail.gmail.com>
On 5/1/18 10:06 AM, Linus Torvalds wrote:
> On Tue, May 1, 2018 at 3:27 AM Tetsuo Handa <
> penguin-kernel@i-love.sakura.ne.jp> wrote:
>
>> Can you review this patch? syzbot has hit this bug for nearly 4000 times
> but
>> is still unable to find a reproducer. Therefore, the only way to test
> would be
>> to apply this patch upstream and test whether the problem is solved.
>
> Looks ok to me, except:
>
>>> smp_wmb();
>>> clear_bit(WB_shutting_down, &wb->state);
>>> + smp_mb(); /* advised by wake_up_bit() */
>>> + wake_up_bit(&wb->state, WB_shutting_down);
>
> This whole sequence really should just be a pattern with a helper function.
>
> And honestly, the pattern probably *should* be
>
> clear_bit_unlock(bit, &mem);
> smp_mb__after_atomic()
> wake_up_bit(&mem, bit);
>
> which looks like it is a bit cleaner wrt memory ordering rules.
Agree, that construct looks saner than introducing a "random"
smp_mb(). As a pattern helper, should probably be introduced
after the fact.
--
Jens Axboe
next prev parent reply other threads:[~2018-05-01 21:31 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-01 17:10 INFO: task hung in wb_shutdown (2) syzbot
2018-04-24 12:19 ` Tetsuo Handa
2018-05-01 10:27 ` Tetsuo Handa
2018-05-01 16:06 ` Linus Torvalds
2018-05-01 21:30 ` Jens Axboe [this message]
2018-05-01 22:14 ` Tetsuo Handa
2018-05-03 15:13 ` Jan Kara
2018-05-03 15:25 ` Jens Axboe
2018-05-01 16:12 ` Jens Axboe
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