[PATCH 3.10 75/85] s390/dasd: hold request queue sysfs lock when calling elevator_init()

[Greg Kroah-Hartman]

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

------------------

From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>

commit ef0899410ff630b2e75306da49996dbbfa318165 upstream.

"elevator: Fix a race in elevator switching and md device initialization"
changed the semantics of elevator_init() in a way that now enforces to hold
the corresponding request queue's sysfs_lock when calling elevator_init()
to fix a race.
The patch did not convert the s390 dasd device driver which is the only
device driver which also calls elevator_init(). So add the missing locking.

Cc: Tomoki Sekiyama <tomoki.sekiyama@xxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Cc: Christian Borntraeger <christian@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/s390/block/dasd.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/s390/block/dasd.c
+++ b/drivers/s390/block/dasd.c
@@ -2879,12 +2879,12 @@ static int dasd_alloc_queue(struct dasd_
 
 	elevator_exit(block->request_queue->elevator);
 	block->request_queue->elevator = NULL;
+	mutex_lock(&block->request_queue->sysfs_lock);
 	rc = elevator_init(block->request_queue, "deadline");
-	if (rc) {
+	if (rc)
 		blk_cleanup_queue(block->request_queue);
-		return rc;
-	}
-	return 0;
+	mutex_unlock(&block->request_queue->sysfs_lock);
+	return rc;
 }
 
 /*


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