[PATCH] block: quiesce queue before freeing queue

There is a race beteewn blk_mq_run_hw_queue() and cleanup queue,
which can cause use-after-free as following:

cpu1                              cpu2
queue_state_write()
                                  blk_release_queue
                                    blk_exit_queue
  blk_mq_run_hw_queue
    blk_mq_hctx_has_pending
      e = q->elevator
                                    q->elevator = NULL
                                    free(q->elevator)
      e && e->type->ops.has_work //use-after-free

Fix this bug by adding quiesce before freeing queue. Then, anyone
who tries to run hw queue will be safe.

This is basically revert of 662156641bc4 ("block: don't drain
in-progress dispatch in blk_cleanup_queue()")

Fixes: 662156641bc4 ("block: don't drain in-progress dispatch in blk_cleanup_queue()")
Signed-off-by: Yufen Yu <redacted>
---
 block/blk-core.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 7663a9b94b80..f8a038d19c89 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c

@@ -392,6 +392,18 @@ void blk_cleanup_queue(struct request_queue *q)
 
 	blk_queue_flag_set(QUEUE_FLAG_DEAD, q);
 
+	/*
+	 * make sure all in-progress dispatch are completed because
+	 * blk_freeze_queue() can only complete all requests, and
+	 * dispatch may still be in-progress since we dispatch requests
+	 * from more than one contexts.
+	 *
+	 * We rely on driver to deal with the race in case that queue
+	 * initialization isn't done.
+	 */
+	if (queue_is_mq(q) && blk_queue_init_done(q))
+		blk_mq_quiesce_queue(q);
+
 	/* for synchronous bio-based driver finish in-flight integrity i/o */
 	blk_flush_integrity();
 

-- 
2.25.4