[PATCH v2 2/6] blk-mq: Fix use after of free q->mq_map

[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 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 releasing q->mq_map in blk_mq_release() to make
it happen latter than removal from all_q_list.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Suggested-by: Ming Lei <tom.leiming@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ming Lei <tom.leiming@gmail.com>
---
 block/blk-mq.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f537796..c5da908 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1928,6 +1928,9 @@ void blk_mq_release(struct request_queue *q)
 		kfree(hctx);
 	}
 
+	kfree(q->mq_map);
+	q->mq_map = NULL;
+
 	kfree(q->queue_hw_ctx);
 
 	/* ctx kobj stays in queue_ctx */
@@ -2073,11 +2076,6 @@ void blk_mq_free_queue(struct request_queue *q)
 	blk_mq_free_hw_queues(q, set);
 
 	percpu_ref_exit(&q->mq_usage_counter);
-
-	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);
-- 
1.9.1