linux-kernel - [PATCH 4.4 068/342] bcache: prevent crash on changing writeback

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Message-Id: <20160301234530.195269446@linuxfoundation.org>
Date:	Tue, 01 Mar 2016 23:54:06 +0000
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	<linux-kernel@...r.kernel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<stable@...r.kernel.org>,
	Stefan Bader <stefan.bader@...onical.com>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Jens Axboe <axboe@...com>
Subject: [PATCH 4.4 068/342] bcache: prevent crash on changing writeback_running

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stefan Bader <stefan.bader@...onical.com>

commit 8d16ce540c94c9d366eb36fc91b7154d92d6397b upstream.

Added a safeguard in the shutdown case. At least while not being
attached it is also possible to trigger a kernel bug by writing into
writeback_running. This change  adds the same check before trying to
wake up the thread for that case.

Signed-off-by: Stefan Bader <stefan.bader@...onical.com>
Cc: Kent Overstreet <kent.overstreet@...il.com>
Signed-off-by: Jens Axboe <axboe@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/bcache/writeback.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -63,7 +63,8 @@ static inline bool should_writeback(stru
 
 static inline void bch_writeback_queue(struct cached_dev *dc)
 {
-	wake_up_process(dc->writeback_thread);
+	if (!IS_ERR_OR_NULL(dc->writeback_thread))
+		wake_up_process(dc->writeback_thread);
 }
 
 static inline void bch_writeback_add(struct cached_dev *dc)