blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter
authorJianchao Wang <jianchao.w.wang@oracle.com>
Tue, 21 Aug 2018 07:15:04 +0000 (15:15 +0800)
committerJens Axboe <axboe@kernel.dk>
Tue, 21 Aug 2018 15:02:56 +0000 (09:02 -0600)
commitf5bbbbe4d63577026f908a809f22f5fd5a90ea1f
treea6d8a1e7329b4160285b79a0565a45b53a2809f6
parentd48ece209f82c9ce07be942441b53d3fa3664936
blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter

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>
block/blk-mq-tag.c
block/blk-mq.c