From: Jianchao Wang Date: Tue, 21 Aug 2018 07:15:04 +0000 (+0800) Subject: blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter X-Git-Tag: v4.19-rc1~56^2~1 X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=f5bbbbe4d635;p=uclinux-h8%2Flinux.git 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 Reviewed-by: Ming Lei Signed-off-by: Jens Axboe --- diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index c0c4e63583ae..8c5cc115b3f8 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -320,6 +320,18 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, 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; @@ -335,7 +347,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, bt_for_each(hctx, &tags->breserved_tags, fn, priv, true); bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false); } - + rcu_read_unlock(); } static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth, diff --git a/block/blk-mq.c b/block/blk-mq.c index 9c8c8c71a13f..81cb84b17b73 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2977,6 +2977,10 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, 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(); + /* * Switch IO scheduler to 'none', cleaning up the data associated * with the previous scheduler. We will switch back once we are done * updating the new sw to hw queue mappings.