[PATCH] blk_execute_rq() oops on fast completion

blk_execute_rq() can oops in wait_for_completion(), if the request has
completed before we call wait_for_completion() because blk_end_sync_rq()
clears ->waiting when it is entered.  Fix this by always using the on-stack
completion variable instead.
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/block/ll_rw_blk.c

@@ -2210,7 +2210,7 @@ int blk_execute_rq(request_queue_t *q, struct gendisk *bd_disk,
 	rq->end_io = blk_end_sync_rq;
 	elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 1);
 	generic_unplug_device(q);
-	wait_for_completion(rq->waiting);
+	wait_for_completion(&wait);
 	rq->waiting = NULL;
 
 	if (rq->errors)