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From: Jan Kara <jack@suse.cz>
To: linux-fsdevel@vger.kernel.org
Cc: linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
	Jan Kara <jack@suse.cz>,
	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
	Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] bdi: Fix oops in wb_workfn()
Date: Wed, 9 May 2018 12:31:35 +0200	[thread overview]
Message-ID: <20180509103135.akgp2u5pzkahji6n@quack2.suse.cz> (raw)
In-Reply-To: <20180503162626.27753-1-jack@suse.cz>

On Thu 03-05-18 18:26:26, Jan Kara wrote:
> Syzbot has reported that it can hit a NULL pointer dereference in
> wb_workfn() due to wb->bdi->dev being NULL. This indicates that
> wb_workfn() was called for an already unregistered bdi which should not
> happen as wb_shutdown() called from bdi_unregister() should make sure
> all pending writeback works are completed before bdi is unregistered.
> Except that wb_workfn() itself can requeue the work with:
> 
> 	mod_delayed_work(bdi_wq, &wb->dwork, 0);
> 
> and if this happens while wb_shutdown() is waiting in:
> 
> 	flush_delayed_work(&wb->dwork);
> 
> the dwork can get executed after wb_shutdown() has finished and
> bdi_unregister() has cleared wb->bdi->dev.
> 
> Make wb_workfn() use wakeup_wb() for requeueing the work which takes all
> the necessary precautions against racing with bdi unregistration.
> 
> CC: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> CC: Tejun Heo <tj@kernel.org>
> Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977
> Reported-by: syzbot <syzbot+9873874c735f2892e7e9@syzkaller.appspotmail.com>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/fs-writeback.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Jens, can you please pick up this patch? Probably for the next merge window
(I don't see a reason to rush this at this point in release cycle). Thanks!

								Honza

> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 47d7c151fcba..471d863958bc 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -1961,7 +1961,7 @@ void wb_workfn(struct work_struct *work)
>  	}
>  
>  	if (!list_empty(&wb->work_list))
> -		mod_delayed_work(bdi_wq, &wb->dwork, 0);
> +		wb_wakeup(wb);
>  	else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
>  		wb_wakeup_delayed(wb);
>  
> -- 
> 2.13.6
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  parent reply	other threads:[~2018-05-09 10:31 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-03 16:26 Jan Kara
2018-05-03 21:55 ` Dave Chinner
2018-05-03 21:57   ` Jens Axboe
2018-05-09  9:48   ` Jan Kara
2018-05-03 22:35 ` Tetsuo Handa
2018-05-09  9:47   ` Jan Kara
2018-05-19 14:27   ` Tetsuo Handa
2018-05-21  9:38     ` Jan Kara
2018-05-25 10:15       ` Tetsuo Handa
2018-05-09 10:31 ` Jan Kara [this message]
2018-05-09 14:42   ` Jens Axboe

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