[PATCH 2/4] blk-mq: fix q->mq_map access race

[Akinobu Mita <akinobu.mita@gmail.com>]

CPU hotplug handling for blk-mq (blk_mq_queue_reinit) updates q->mq_map
by blk_mq_update_queue_map() for all request queues in all_q_list.
On the other hand, q->mq_map is released and set to NULL before
deleting the queue from all_q_list.

So if cpu hotplug event occurs in the window, invalid memory access
can happen.  Fix it by deleting the queue from all_q_list earlier
than destroyng q->mq_map.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
---
 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 ec94258..6487710 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2038,6 +2038,10 @@ 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);
@@ -2048,10 +2052,6 @@ void blk_mq_free_queue(struct request_queue *q)
 	kfree(q->mq_map);
 
 	q->mq_map = NULL;
-
-	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 */
-- 
1.9.1

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