From: Keith Busch <kbusch@kernel.org>
Date: Tue, 11 Nov 2025 14:06:20 +0000 (-0800)
Subject: block: fix merging data-less bios
X-Git-Tag: v6.19-rc1~168^2~58
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fd9ecd005252b595fd02ff7fcc4056251027404d;p=thirdparty%2Fkernel%2Flinux.git

block: fix merging data-less bios

The data segment gaps the block layer tracks doesn't apply to bio's that
don't have data. Skip calculating this to fix a NULL pointer access.

Fixes: 2f6b2565d43cdb5 ("block: accumulate memory segment gaps per bio")
Reported-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Yu Kuai <yukuai@fnnas.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 3ca6fbf8b7870..d3115d7469df0 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -737,6 +737,9 @@ u8 bio_seg_gap(struct request_queue *q, struct bio *prev, struct bio *next,
 {
 	struct bio_vec pb, nb;
 
+	if (!bio_has_data(prev))
+		return 0;
+
 	gaps_bit = min_not_zero(gaps_bit, prev->bi_bvec_gap_bit);
 	gaps_bit = min_not_zero(gaps_bit, next->bi_bvec_gap_bit);