From: Kent Overstreet <kent.overstreet@gmail.com>
Date: Tue, 8 May 2018 21:33:56 -0400
Subject: [PATCH] block: Add warning for bi_next not NULL in bio_endio()
Git-commit: 0ba99ca4838bc75481a4bf0e70bad20b0a5457c7
Patch-mainline: v4.18-rc1
References: bsc#1104967,FATE#325924

Recently found a bug where a driver left bi_next not NULL and then
called bio_endio(), and then the submitter of the bio used
bio_copy_data() which was treating src and dst as lists of bios.

Fixed that bug by splitting out bio_list_copy_data(), but in case other
things are depending on bi_next in weird ways, add a warning to help
avoid more bugs like that in the future.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 block/bio.c      | 3 +++
 block/blk-core.c | 8 +++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index 2112ad01b52c..d8bcc12d5aa4 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1775,6 +1775,9 @@ void bio_endio(struct bio *bio)
 	if (!bio_integrity_endio(bio))
 		return;
 
+	if (WARN_ONCE(bio->bi_next, "driver left bi_next not NULL"))
+		bio->bi_next = NULL;
+
 	/*
 	 * Need to have a real endio function for chained bios, otherwise
 	 * various corner cases will break (like stacking block devices that
diff --git a/block/blk-core.c b/block/blk-core.c
index b431558f39bc..43370faee935 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -279,6 +279,10 @@ static void req_bio_endio(struct request *rq, struct bio *bio,
 	bio_advance(bio, nbytes);
 
 	/* don't actually finish bio if it's part of flush sequence */
+	/*
+	 * XXX this code looks suspicious - it's not consistent with advancing
+	 * req->bio in caller
+	 */
 	if (bio->bi_iter.bi_size == 0 && !(rq->rq_flags & RQF_FLUSH_SEQ))
 		bio_endio(bio);
 }
@@ -3083,8 +3087,10 @@ bool blk_update_request(struct request *req, blk_status_t error,
 		struct bio *bio = req->bio;
 		unsigned bio_bytes = min(bio->bi_iter.bi_size, nr_bytes);
 
-		if (bio_bytes == bio->bi_iter.bi_size)
+		if (bio_bytes == bio->bi_iter.bi_size) {
 			req->bio = bio->bi_next;
+			bio->bi_next = NULL;
+		}
 
 		/* Completion has already been traced */
 		bio_clear_flag(bio, BIO_TRACE_COMPLETION);
-- 
2.12.3