Add a comment above the queue_lockdep_assert_held() macro that
explains the purpose of the q->queue_lock test.
Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Omar Sandoval <osandov@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
---
include/linux/blkdev.h | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8a223a0c95d5..293067a2726e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -634,6 +634,13 @@ struct request_queue {
(1 << QUEUE_FLAG_SAME_COMP) | \
(1 << QUEUE_FLAG_POLL))
+/*
+ * @q->queue_lock is set while a queue is being initialized. Since we know
+ * that no other threads access the queue object before @q->queue_lock has
+ * been set, it is safe to manipulate queue flags without holding the
+ * queue_lock if @q->queue_lock == NULL. See also blk_alloc_queue_node() and
+ * blk_init_allocated_queue().
+ */
static inline void queue_lockdep_assert_held(struct request_queue *q)
{
if (q->queue_lock)
--
2.12.2
