[PATCH 3.16.y-ckt 133/142] bcache: add mutex lock for bch_is_open

[Luis Henriques]

3.16.7-ckt26 -stable review patch.  If anyone has any objections, please let me know.

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

From: Jianjian Huo <samuel.huo at gmail.com>

commit 789d21dbd9d8889e62c79ec19585fcc97e42ef07 upstream.

Since bch_is_open will iterate linked list bch_cache_sets and
uncached_devices, it needs bch_register_lock.

Signed-off-by: Jianjian Huo <samuel.huo at gmail.com>
Cc: Kamal Mostafa <kamal at canonical.com>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/md/bcache/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 72e660cafadd..70db24e41947 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1950,10 +1950,12 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 	if (IS_ERR(bdev)) {
 		if (bdev == ERR_PTR(-EBUSY)) {
 			bdev = lookup_bdev(strim(path));
+			mutex_lock(&bch_register_lock);
 			if (!IS_ERR(bdev) && bch_is_open(bdev))
 				err = "device already registered";
 			else
 				err = "device busy";
+			mutex_unlock(&bch_register_lock);
 			if (attr == &ksysfs_register_quiet)
 				goto out;
 		}