[PATCH] block: mark flush request as IDLE when it is really finished

[Ming Lei <ming.lei@redhat.com>]

For avoiding use-after-free on flush request, we call its .end_io() from
both timeout code path and __blk_mq_end_request().

When flush request's ref doesn't drop to zero, it is still used, we
can't mark it as IDLE, so fix it by marking IDLE when its refcount drops
to zero really.

Fixes: 65ff5cd04551 ("blk-mq: mark flush request as IDLE in flush_end_io()")
Cc: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-flush.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/block/blk-flush.c b/block/blk-flush.c
index c64f049226f6..23124d60cffe 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -224,13 +224,18 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error)
 	/* release the tag's ownership to the req cloned from */
 	spin_lock_irqsave(&fq->mq_flush_lock, flags);
 
-	WRITE_ONCE(flush_rq->state, MQ_RQ_IDLE);
 	if (!refcount_dec_and_test(&flush_rq->ref)) {
 		fq->rq_status = error;
 		spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 		return;
 	}
 
+	/*
+	 * Flush request has to be marked as IDLE when it is really ended
+	 * because its .end_io() is called from timeout code path too for
+	 * avoiding use-after-free.
+	 */
+	WRITE_ONCE(flush_rq->state, MQ_RQ_IDLE);
 	if (fq->rq_status != BLK_STS_OK)
 		error = fq->rq_status;
 
-- 
2.25.4