[added to the 4.1 stable tree] bcache: allows use of register in udev to avoid "device_busy" error.

From: Gabriel de Perthuis <redacted>

This patch has been added to the 4.1 stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit d7076f21629f8f329bca4a44dc408d94670f49e2 ]

Allows to use register, not register_quiet in udev to avoid "device_busy" error.
The initial patch proposed at https://lkml.org/lkml/2013/8/26/549 by Gabriel de Perthuis
[off-list ref] does not unlock the mutex and hangs the kernel.

See http://thread.gmane.org/gmane.linux.kernel.bcache.devel/2594 for the discussion.

Cc: Denis Bychkov <redacted>
Cc: Kent Overstreet <redacted>
Cc: Eric Wheeler <redacted>
Cc: Gabriel de Perthuis <redacted>
Cc: stable@vger.kernel.org

Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Sasha Levin <redacted>
---
 drivers/md/bcache/super.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 53f1512..42522c8 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c

@@ -1972,6 +1972,8 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 			else
 				err = "device busy";
 			mutex_unlock(&bch_register_lock);
+			if (attr == &ksysfs_register_quiet)
+				goto out;
 		}
 		goto err;
 	}

@@ -2010,8 +2012,7 @@ out:
 err_close:
 	blkdev_put(bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
 err:
-	if (attr != &ksysfs_register_quiet)
-		pr_info("error opening %s: %s", path, err);
+	pr_info("error opening %s: %s", path, err);
 	ret = -EINVAL;
 	goto out;
 }

-- 
2.5.0