From: Ming Lei <ming.lei@redhat.com>
Date: Fri, 13 Nov 2020 21:44:48 +0800
Subject: block: mark flush request as IDLE when it is really finished
Patch-mainline: v5.10-rc5
Git-commit: 9f16a66733c90b5f33f624b0b0e36a345b0aaf93
References: bsc#1193787

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()")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Cc: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 block/blk-flush.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -225,13 +225,18 @@ static void flush_end_io(struct request
 	/* 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;