* [PATCH RESEND] block: fix discard request merge
@ 2021-06-28 2:33 Ming Lei
2021-06-29 13:41 ` Jens Axboe
0 siblings, 1 reply; 2+ messages in thread
From: Ming Lei @ 2021-06-28 2:33 UTC (permalink / raw
To: Jens Axboe; +Cc: linux-block, Ming Lei, Christoph Hellwig, Wang Shanker
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>
---
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 5c9d2a4ece86..a4afa488298e 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -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;
/*
--
2.31.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH RESEND] block: fix discard request merge
2021-06-28 2:33 [PATCH RESEND] block: fix discard request merge Ming Lei
@ 2021-06-29 13:41 ` Jens Axboe
0 siblings, 0 replies; 2+ messages in thread
From: Jens Axboe @ 2021-06-29 13:41 UTC (permalink / raw
To: Ming Lei; +Cc: linux-block, Christoph Hellwig, Wang Shanker
On 6/27/21 8:33 PM, Ming Lei wrote:
> 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.
Applied, thanks.
--
Jens Axboe
^ permalink raw reply [flat|nested] 2+ messages in thread
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2021-06-29 13:41 ` Jens Axboe
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