linux-kernel - [PATCH] block: fix unexpected split in bio_discard

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Date:   Thu, 17 Aug 2023 15:55:06 +0800
From:   Li Feng <fengli@...rtx.com>
To:     Jens Axboe <axboe@...nel.dk>,
        linux-block@...r.kernel.org (open list:BLOCK LAYER),
        linux-kernel@...r.kernel.org (open list)
Cc:     lifeng1519@...il.com, Li Feng <fengli@...rtx.com>
Subject: [PATCH] block: fix unexpected split in bio_discard_limit

bio_discard_limit() enforces discard boundaries within the range of 32-bit
unsigned integers, resulting in unexpected discard cut boundaries.

For example, max discard size = 1MiB, discard_granularity = 512B, then the
discard lengths sent in the range [0,4G) are 1MiB, 1MiB... (1MiB-512).
The next discard offset from 4G is [4G-512, 4G-512+1MiB).
The discard of the 4G offset boundary does not comply with the optimal 1MiB
size.

Signed-off-by: Li Feng <fengli@...rtx.com>
---
 block/blk-lib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index e59c3069e835..ec95508c3593 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -32,7 +32,7 @@ static sector_t bio_discard_limit(struct block_device *bdev, sector_t sector)
 	 * Align the bio size to the discard granularity to make splitting the bio
 	 * at discard granularity boundaries easier in the driver if needed.
 	 */
-	return round_down(UINT_MAX, discard_granularity) >> SECTOR_SHIFT;
+	return round_down(ULONG_MAX, discard_granularity) >> SECTOR_SHIFT;
 }
 
 int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
-- 
2.41.0