Instead of returning an inconclusive value of NULL for an error in calling
bio_split(), return a ERR_PTR() always.

Also remove the BUG_ON() calls, and WARN_ON_ONCE() instead. Indeed, since
almost all callers don't check the return code from bio_split(), we'll
crash anyway (for those failures).

Fix up the only user which checks bio_split() return code today (directly
or indirectly), blk_crypto_fallback_split_bio_if_needed(). The md/bcache
code does check the return code in cached_dev_cache_miss() ->
bio_next_split() -> bio_split(), but only to see if there was a split, so
there would be no change in behaviour here (when returning a ERR_PTR()).

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 block/bio.c                 | 10 ++++++----
 block/blk-crypto-fallback.c |  2 +-
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 4cc33ee68640..42cac7c46e55 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1740,16 +1740,18 @@ struct bio *bio_split(struct bio *bio, int sectors,
 {
 	struct bio *split;
 
-	BUG_ON(sectors <= 0);
-	BUG_ON(sectors >= bio_sectors(bio));
+	if (WARN_ON_ONCE(sectors <= 0))
+		return ERR_PTR(-EINVAL);
+	if (WARN_ON_ONCE(sectors >= bio_sectors(bio)))
+		return ERR_PTR(-EINVAL);
 
 	/* Zone append commands cannot be split */
 	if (WARN_ON_ONCE(bio_op(bio) == REQ_OP_ZONE_APPEND))
-		return NULL;
+		return ERR_PTR(-EINVAL);
 
 	split = bio_alloc_clone(bio->bi_bdev, bio, gfp, bs);
 	if (!split)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	split->bi_iter.bi_size = sectors << 9;
 
diff --git a/block/blk-crypto-fallback.c b/block/blk-crypto-fallback.c
index b1e7415f8439..29a205482617 100644
--- a/block/blk-crypto-fallback.c
+++ b/block/blk-crypto-fallback.c
@@ -226,7 +226,7 @@ static bool blk_crypto_fallback_split_bio_if_needed(struct bio **bio_ptr)
 
 		split_bio = bio_split(bio, num_sectors, GFP_NOIO,
 				      &crypto_bio_split);
-		if (!split_bio) {
+		if (IS_ERR(split_bio)) {
 			bio->bi_status = BLK_STS_RESOURCE;
 			return false;
 		}
-- 
2.31.1

Looks good,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

(hopefully I'll remember the change when I forward port my new code
using it :))