Merge tag 'for-4.19/post-20180822' of git://git.kernel.dk/linux-block

[sfrench/cifs-2.6.git] / block / blk-mq-tag.c

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 816923bf874d7c8eb55ed640735caab5131022a4..94e1ed667b6ea383a99f1cd76d6917af0d2a1ba6 100644 (file)
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -320,6 +320,18 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
        struct blk_mq_hw_ctx *hctx;
        int i;
 
+       /*
+        * __blk_mq_update_nr_hw_queues will update the nr_hw_queues and
+        * queue_hw_ctx after freeze the queue. So we could use q_usage_counter
+        * to avoid race with it. __blk_mq_update_nr_hw_queues will users
+        * synchronize_rcu to ensure all of the users go out of the critical
+        * section below and see zeroed q_usage_counter.
+        */
+       rcu_read_lock();
+       if (percpu_ref_is_zero(&q->q_usage_counter)) {
+               rcu_read_unlock();
+               return;
+       }
 
        queue_for_each_hw_ctx(q, hctx, i) {
                struct blk_mq_tags *tags = hctx->tags;
@@ -335,7 +347,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
                        bt_for_each(hctx, &tags->breserved_tags, fn, priv, true);
                bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false);
        }
-
+       rcu_read_unlock();
 }
 
 static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,