From 0e6263682014d480b8d7b8c10287f4536066b54f Mon Sep 17 00:00:00 2001 From: Akinobu Mita Date: Sun, 27 Sep 2015 02:09:22 +0900 Subject: [PATCH] blk-mq: fix q->mq_usage_counter access race CPU hotplug handling for blk-mq (blk_mq_queue_reinit) accesses q->mq_usage_counter while freezing all request queues in all_q_list. On the other hand, q->mq_usage_counter is deinitialized in blk_mq_free_queue() before deleting the queue from all_q_list. So if CPU hotplug event occurs in the window, percpu_ref_kill() is called with q->mq_usage_counter which has already been marked dead, and it triggers warning. Fix it by deleting the queue from all_q_list earlier than destroying q->mq_usage_counter. Signed-off-by: Akinobu Mita Reviewed-by: Ming Lei Cc: Ming Lei Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- block/blk-mq.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 92648d8d6a4a..3a39184e82e5 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2067,15 +2067,16 @@ void blk_mq_free_queue(struct request_queue *q) { struct blk_mq_tag_set *set = q->tag_set; + mutex_lock(&all_q_mutex); + list_del_init(&q->all_q_node); + mutex_unlock(&all_q_mutex); + blk_mq_del_queue_tag_set(q); blk_mq_exit_hw_queues(q, set, set->nr_hw_queues); blk_mq_free_hw_queues(q, set); percpu_ref_exit(&q->mq_usage_counter); - mutex_lock(&all_q_mutex); - list_del_init(&q->all_q_node); - mutex_unlock(&all_q_mutex); } /* Basically redo blk_mq_init_queue with queue frozen */