commit 0e6263682014d480b8d7b8c10287f4536066b54f
author Akinobu Mita <akinobu.mita@gmail.com> Sun Sep 27 02:09:22 2015 +0900
committer Jens Axboe <axboe@fb.com> Tue Sep 29 11:32:48 2015 -0600
tree 6ebd842a4a9ef717cfc4a05c99fddede9fb4328e
parent a723bab3d7529133f71fc8a5e96f86e3639a0d13

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 <akinobu.mita@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>