[PATCH 4.2.y-ckt 075/268] bcache: prevent crash on changing writeback_running

From: Kamal Mostafa
Date: Wed Jan 27 2016 - 16:46:00 EST

4.2.8-ckt3 -stable review patch. If anyone has any objections, please let me know.


From: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
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 0a9dab1..073a042 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)