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block: fix discard request merge 

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>
This commit is contained in:
Ming Lei 2021-06-28 10:33:12 +08:00 committed by Jens Axboe
parent c06bc5a3fb
commit 2705dfb209
1 changed files with 6 additions and 2 deletions
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8
block/blk-merge.c
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@ -559,10 +559,14 @@ 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;
/*