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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Jens Axboe <axboe@kernel.dk>, 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, 01 May 2018 16:06:48 +0000	[thread overview]
Message-ID: <CA+55aFxaa_+uZ=bOVdevcUwG7ncue7O+i06q4Kb=bWACGwCBjQ@mail.gmail.com> (raw)
In-Reply-To: <43302799-1c50-4cab-b974-9fe1ca584813@I-love.SAKURA.ne.jp>

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.

             Linus

  reply	other threads:[~2018-05-01 16:06 UTC|newest]

Thread overview: 13+ 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
2018-04-24 12:19   ` Tetsuo Handa
2018-05-01 10:27   ` Tetsuo Handa
2018-05-01 10:27     ` Tetsuo Handa
2018-05-01 16:06     ` Linus Torvalds [this message]
2018-05-01 21:30       ` Jens Axboe
2018-05-01 22:14         ` Tetsuo Handa
2018-05-01 22:14           ` Tetsuo Handa
2018-05-03 15:13           ` Jan Kara
2018-05-03 15:25           ` Jens Axboe
2018-05-03 15:25             ` Jens Axboe
2018-05-01 16:12     ` Jens Axboe

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