blk-mq: Fix use after of free q->mq_map

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>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Cc: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0262131ac5f2..92648d8d6a4a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1925,6 +1925,9 @@ 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 */
@@ -2070,11 +2073,6 @@ 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);