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.

Backporting Notes

This is a re-backport, landing synchronize_rcu in the right place.

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 Signed-off-by: Giuliano Procida gprocida@google.com --- block/blk-mq.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c index 58be2eaa5aaa..e0ed7317e98c 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2331,6 +2331,10 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)

list_for_each_entry(q, &set->tag_list, tag_set_list) blk_mq_freeze_queue(q); + /* + * Sync with blk_mq_queue_tag_busy_iter. + */ + synchronize_rcu();

set->nr_hw_queues = nr_hw_queues; list_for_each_entry(q, &set->tag_list, tag_set_list) { @@ -2346,10 +2350,6 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)

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);