From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: syzbot <syzbot+4a7438e774b21ddd8eca@syzkaller.appspotmail.com>,
syzkaller-bugs@googlegroups.com, jack@suse.cz
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
viro@zeniv.linux.org.uk, axboe@kernel.dk, tj@kernel.org,
david@fromorbit.com, linux-block@vger.kernel.org
Subject: [PATCH] bdi: Fix another oops in wb_workfn()
Date: Sun, 27 May 2018 11:21:25 +0900 [thread overview]
Message-ID: <314ae2e0-c873-04ce-9cd5-fe2acadaee26@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <0c7c5dea-7312-8a59-9d1b-5467f69719bf@I-love.SAKURA.ne.jp>
>From 8a8222698163d1fe180258566e9a3ff43f54fcd9 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sun, 27 May 2018 11:08:20 +0900
Subject: [PATCH] bdi: Fix another oops in wb_workfn()
syzbot is still hitting NULL pointer dereference at wb_workfn() [1].
This might be because we overlooked that delayed_work_timer_fn() does not
check WB_registered before calling __queue_work() while mod_delayed_work()
does not wait for already started delayed_work_timer_fn() because it uses
del_timer() rather than del_timer_sync().
Make wb_shutdown() be careful about wb_wakeup_delayed() path.
[1] https://syzkaller.appspot.com/bug?id=e0818ccb7e46190b3f1038b0c794299208ed4206
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+4a7438e774b21ddd8eca@syzkaller.appspotmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
---
mm/backing-dev.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 7441bd9..31e1d7e 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -372,11 +372,24 @@ static void wb_shutdown(struct bdi_writeback *wb)
cgwb_remove_from_bdi_list(wb);
/*
+ * mod_delayed_work() is not appropriate here, for
+ * delayed_work_timer_fn() from wb_wakeup_delayed() does not check
+ * WB_registered before calling __queue_work().
+ */
+ del_timer_sync(&wb->dwork.timer);
+ /*
+ * Clear WORK_STRUCT_PENDING_BIT in order to make sure that next
+ * queue_delayed_work() actually enqueues this work to the tail, for
+ * wb_wakeup_delayed() already set WORK_STRUCT_PENDING_BIT before
+ * scheduling delayed_work_timer_fn().
+ */
+ cancel_delayed_work_sync(&wb->dwork);
+ /*
* Drain work list and shutdown the delayed_work. !WB_registered
* tells wb_workfn() that @wb is dying and its work_list needs to
* be drained no matter what.
*/
- mod_delayed_work(bdi_wq, &wb->dwork, 0);
+ queue_delayed_work(bdi_wq, &wb->dwork, 0);
flush_delayed_work(&wb->dwork);
WARN_ON(!list_empty(&wb->work_list));
/*
--
1.8.3.1
next prev parent reply other threads:[~2018-05-27 2:22 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-26 9:15 general protection fault in wb_workfn (2) syzbot
2018-05-27 0:47 ` Tetsuo Handa
2018-05-27 2:21 ` Tetsuo Handa [this message]
2018-05-27 2:36 ` [PATCH] bdi: Fix another oops in wb_workfn() Tejun Heo
2018-05-28 13:35 ` general protection fault in wb_workfn (2) Jan Kara
2018-05-30 16:00 ` Tetsuo Handa
2018-05-31 11:42 ` Jan Kara
2018-05-31 13:19 ` Tetsuo Handa
2018-05-31 13:42 ` Jan Kara
2018-05-31 16:56 ` Jens Axboe
2018-06-05 13:45 ` Tetsuo Handa
2018-06-07 18:46 ` Dmitry Vyukov
2018-06-08 2:31 ` Tetsuo Handa
2018-06-08 14:45 ` Dmitry Vyukov
2018-06-08 15:16 ` Dmitry Vyukov
2018-06-08 16:53 ` Dmitry Vyukov
2018-06-08 17:14 ` Dmitry Vyukov
2018-06-09 5:30 ` Tetsuo Handa
2018-06-09 14:00 ` [PATCH] bdi: Fix another oops in wb_workfn() Tetsuo Handa
2018-06-11 9:12 ` Jan Kara
2018-06-11 16:01 ` Tejun Heo
2018-06-11 16:29 ` Jan Kara
2018-06-11 17:20 ` Tejun Heo
2018-06-12 15:57 ` Jan Kara
2018-06-13 10:43 ` Tetsuo Handa
2018-06-13 11:51 ` Tetsuo Handa
2018-06-13 14:06 ` Linus Torvalds
2018-06-13 14:46 ` Jan Kara
2018-06-13 14:55 ` Linus Torvalds
2018-06-13 16:20 ` Tetsuo Handa
2018-06-13 16:25 ` Linus Torvalds
2018-06-13 16:45 ` Jan Kara
2018-06-13 21:04 ` Tetsuo Handa
2018-06-14 10:11 ` Jan Kara
2018-06-13 14:33 ` Tejun Heo
2018-06-15 12:06 ` Jan Kara
2018-06-18 12:27 ` Jan Kara
2018-06-01 2:30 ` general protection fault in wb_workfn (2) Dave Chinner
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