block: use atomic bitops for ->queue_flags

->queue_flags is generally not set or cleared in the fast path, and also
generally set or cleared one flag at a time.  Make use of the normal
atomic bitops for it so that we don't need to take the queue_lock,
which is otherwise mostly unused in the core block layer now.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-settings.c b/block/blk-settings.c
index cca8359..3abe831 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -834,16 +834,14 @@ EXPORT_SYMBOL(blk_set_queue_depth);
  */
 void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
 {
-	spin_lock_irq(q->queue_lock);
 	if (wc)
-		queue_flag_set(QUEUE_FLAG_WC, q);
+		blk_queue_flag_set(QUEUE_FLAG_WC, q);
 	else
-		queue_flag_clear(QUEUE_FLAG_WC, q);
+		blk_queue_flag_clear(QUEUE_FLAG_WC, q);
 	if (fua)
-		queue_flag_set(QUEUE_FLAG_FUA, q);
+		blk_queue_flag_set(QUEUE_FLAG_FUA, q);
 	else
-		queue_flag_clear(QUEUE_FLAG_FUA, q);
-	spin_unlock_irq(q->queue_lock);
+		blk_queue_flag_clear(QUEUE_FLAG_FUA, q);
 
 	wbt_set_write_cache(q, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
 }