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: [PATCH] bdi: Fix oops in wb_workfn()
Date: Thu, 3 May 2018 18:26:26 +0200 [thread overview]
Message-ID: <20180503162626.27753-1-jack@suse.cz> (raw)
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(-)
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
next reply other threads:[~2018-05-03 16:26 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-03 16:26 Jan Kara [this message]
2018-05-03 21:55 ` [PATCH] bdi: Fix oops in wb_workfn() 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
2018-05-09 14:42 ` Jens Axboe
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