[PATCH 1/6] blk-mq: Make blk_mq_quiesce_queue() wait for all .queue_rq() calls

[Bart Van Assche <bart.vanassche@sandisk.com>]

blk_mq_quiesce_queue() callers, e.g. elevator_switch_mq(), assume
that no .queue_rq() calls occur while switching to another I/O
scheduler. This patch fixes the following kernel crash if another
I/O scheduler than "none" is the default scheduler:

general protection fault: 0000 [#1] SMP
RIP: 0010:__lock_acquire+0xfe/0x1280
Call Trace:
 lock_acquire+0xd5/0x1c0
 _raw_spin_lock+0x2a/0x40
 dd_dispatch_request+0x29/0x1e0
 blk_mq_sched_dispatch_requests+0x139/0x190
 __blk_mq_run_hw_queue+0x12d/0x1c0
 blk_mq_run_work_fn+0xd/0x10
 process_one_work+0x206/0x6a0
 worker_thread+0x49/0x4a0
 kthread+0x107/0x140
 ret_from_fork+0x2e/0x40

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: <stable@vger.kernel.org>
---
 block/blk-mq.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index b75ef2392db7..3b3420f76b5a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1224,8 +1224,9 @@ EXPORT_SYMBOL(blk_mq_queue_stopped);
 
 void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx)
 {
-	cancel_work(&hctx->run_work);
-	cancel_delayed_work(&hctx->delay_work);
+	cancel_work_sync(&hctx->run_work);
+	cancel_delayed_work_sync(&hctx->delay_work);
+	cancel_delayed_work_sync(&hctx->delayed_run_work);
 	set_bit(BLK_MQ_S_STOPPED, &hctx->state);
 }
 EXPORT_SYMBOL(blk_mq_stop_hw_queue);
-- 
2.12.2