linux-kernel - [PATCH 3.16.y-ckt 066/180] bcache: prevent crash on changing writeback

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Message-Id: <1454538786-12215-67-git-send-email-luis.henriques@canonical.com>
Date:	Wed,  3 Feb 2016 22:31:12 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Stefan Bader <stefan.bader@...onical.com>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Jens Axboe <axboe@...com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 066/180] bcache: prevent crash on changing writeback_running

3.16.7-ckt24 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

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: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/md/bcache/writeback.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h
index e2f8598937ac..afe7ecada503 100644
--- a/drivers/md/bcache/writeback.h
+++ b/drivers/md/bcache/writeback.h
@@ -63,7 +63,8 @@ static inline bool should_writeback(struct cached_dev *dc, struct bio *bio,
 
 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)