commit 530ca2c9bd6949c72c9b5cfc330cb3dbccaa3f5b upstream.
A recent commit runs tag iterator callbacks under the rcu read lock,
but existing callbacks do not satisfy the non-blocking requirement.
The commit intended to prevent an iterator from accessing a queue that's
being modified. This patch fixes the original issue by taking a queue
reference instead of reading it, which allows callbacks to make blocking
calls.
Fixes: f5bbbbe4d6357 ("blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter")
Acked-by: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx>
Signed-off-by: Keith Busch <keith.busch@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Giuliano Procida <gprocida@xxxxxxxxxx>
---
block/blk-mq-tag.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index bf356de30134..c1c654319287 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -484,11 +484,8 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
/*
* Avoid potential races with things like queue removal.
*/
- rcu_read_lock();
- if (percpu_ref_is_zero(&q->q_usage_counter)) {
- rcu_read_unlock();
+ if (!percpu_ref_tryget(&q->q_usage_counter))
return;
- }
queue_for_each_hw_ctx(q, hctx, i) {
struct blk_mq_tags *tags = hctx->tags;
@@ -505,7 +502,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
bt_for_each(hctx, &tags->bitmap_tags, tags->nr_reserved_tags, fn, priv,
false);
}
- rcu_read_unlock();
+ blk_queue_exit(q);
}
static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)
--
2.26.0.110.g2183baf09c-goog
