[PATCH 08/10] block: Add warning for bi_next not NULL in bio_endio()

Kent Overstreet
2018-05-09T01:33:56Z

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>
---
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 ce8e259f9a..5c81391100 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 66f24798ef..f3cf79198a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -204,6 +204,10 @@ 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);
}
@@ -2982,8 +2986,10 @@ 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);
--
2.17.0