scsi: block: Add a helper to cancel atomic queue limit updates

Drivers might have to perform complex actions to determine queue limits,
and those might fail. Add a helper to cancel a queue limit update that can
be called in those cases.

Signed-off-by: Christoph Hellwig <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Kanchan Joshi <[e-mail]>
Reviewed-by: Damien Le Moal <[e-mail]>
Reviewed-by: Hannes Reinecke <[e-mail]>
Reviewed-by: John Garry <[e-mail]>
Reviewed-by: Johannes Thumshirn <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

include/linux/blkdev.h

···
 		struct queue_limits *lim);
 int queue_limits_set(struct request_queue *q, struct queue_limits *lim);
 
+/**
+ * queue_limits_cancel_update - cancel an atomic update of queue limits
+ * @q:		queue to update
+ *
+ * This functions cancels an atomic update of the queue limits started by
+ * queue_limits_start_update() and should be used when an error occurs after
+ * starting update.
+ */
+static inline void queue_limits_cancel_update(struct request_queue *q)
+{
+	mutex_unlock(&q->limits_lock);
+}
+
 /*
  * Access functions for manipulating queue properties
  */