From: Jianchao Wang jianchao.w.wang@oracle.com
commit f5bbbbe4d63577026f908a809f22f5fd5a90ea1f upstream.
For blk-mq, part_in_flight/rw will invoke blk_mq_in_flight/rw to account the inflight requests. It will access the queue_hw_ctx and nr_hw_queues w/o any protection. When updating nr_hw_queues and blk_mq_in_flight/rw occur concurrently, panic comes up.
Before update nr_hw_queues, the q will be frozen. So we could use q_usage_counter to avoid the race. percpu_ref_is_zero is used here so that we will not miss any in-flight request. The access to nr_hw_queues and queue_hw_ctx in blk_mq_queue_tag_busy_iter are under rcu critical section, __blk_mq_update_nr_hw_queues could use synchronize_rcu to ensure the zeroed q_usage_counter to be globally visible.
Signed-off-by: Jianchao Wang jianchao.w.wang@oracle.com Reviewed-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Cc: Giuliano Procida gprocida@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- block/blk-mq-tag.c | 14 +++++++++++++- block/blk-mq.c | 4 ++++ 2 files changed, 17 insertions(+), 1 deletion(-)
--- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -336,6 +336,18 @@ void blk_mq_queue_tag_busy_iter(struct r 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; @@ -351,7 +363,7 @@ void blk_mq_queue_tag_busy_iter(struct r bt_for_each(hctx, &tags->breserved_tags, fn, priv, true); bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false); } - + rcu_read_unlock(); }
static unsigned int bt_unused_tags(const struct sbitmap_queue *bt) --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2346,6 +2346,10 @@ void blk_mq_update_nr_hw_queues(struct b
list_for_each_entry(q, &set->tag_list, tag_set_list) blk_mq_unfreeze_queue(q); + /* + * Sync with blk_mq_queue_tag_busy_iter. + */ + synchronize_rcu(); } EXPORT_SYMBOL_GPL(blk_mq_update_nr_hw_queues);