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-rw-r--r--block/blk-mq.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index aa9a05fdd023..a4c54c5895a1 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1853,6 +1853,22 @@ static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx,
__add_wait_queue(wq, wait);
/*
+ * Add one explicit barrier since blk_mq_get_driver_tag() may
+ * not imply barrier in case of failure.
+ *
+ * Order adding us to wait queue and allocating driver tag.
+ *
+ * The pair is the one implied in sbitmap_queue_wake_up() which
+ * orders clearing sbitmap tag bits and waitqueue_active() in
+ * __sbitmap_queue_wake_up(), since waitqueue_active() is lockless
+ *
+ * Otherwise, re-order of adding wait queue and getting driver tag
+ * may cause __sbitmap_queue_wake_up() to wake up nothing because
+ * the waitqueue_active() may not observe us in wait queue.
+ */
+ smp_mb();
+
+ /*
* It's possible that a tag was freed in the window between the
* allocation failure and adding the hardware queue to the wait
* queue.