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Subject[PATCH AUTOSEL 5.4 23/26] block: fix discard request merge
Date
From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit 2705dfb2094777e405e065105e307074af8965c1 ]

ll_new_hw_segment() is reached only in case of single range discard
merge, and we don't have max discard segment size limit actually, so
it is wrong to run the following check:

if (req->nr_phys_segments + nr_phys_segs > blk_rq_get_max_segments(req))

it may be always false since req->nr_phys_segments is initialized as
one, and bio's segment count is still 1, blk_rq_get_max_segments(reg)
is 1 too.

Fix the issue by not doing the check and bypassing the calculation of
discard request's nr_phys_segments.

Based on analysis from Wang Shanker.

Cc: Christoph Hellwig <hch@lst.de>
Reported-by: Wang Shanker <shankerwangmiao@gmail.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210628023312.1903255-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-merge.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 03959bfe961c..4b022f0c49d2 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -571,10 +571,14 @@ static inline unsigned int blk_rq_get_max_segments(struct request *rq)
static inline int ll_new_hw_segment(struct request *req, struct bio *bio,
unsigned int nr_phys_segs)
{
- if (req->nr_phys_segments + nr_phys_segs > blk_rq_get_max_segments(req))
+ if (blk_integrity_merge_bio(req->q, req, bio) == false)
goto no_merge;

- if (blk_integrity_merge_bio(req->q, req, bio) == false)
+ /* discard request merge won't add new segment */
+ if (req_op(req) == REQ_OP_DISCARD)
+ return 1;
+
+ if (req->nr_phys_segments + nr_phys_segs > blk_rq_get_max_segments(req))
goto no_merge;

/*
--
2.30.2
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