[3.13.y-ckt stable] Patch "bcache: prevent crash on changing writeback_running" has been added to the 3.13.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    bcache: prevent crash on changing writeback_running

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt34.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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

>From 8124c3693a68f8917c1908348196714e5107a15e Mon Sep 17 00:00:00 2001
From: Stefan Bader <stefan.bader at canonical.com>
Date: Sun, 29 Nov 2015 18:44:49 -0800
Subject: bcache: prevent crash on changing writeback_running

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 at canonical.com>
Cc: Kent Overstreet <kent.overstreet at gmail.com>
Signed-off-by: Jens Axboe <axboe at fb.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.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 c9ddcf4..2a94fa3 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)
--
1.9.1