bio_discard_limit() uses round_up() and round_down(), which require a
power-of-two alignment. However, discard_granularity need not be a power
of two. For example, dm-thin supports data block sizes that are arbitrary
multiples of 64 KiB and advertises the block size as its granularity.
With a 192 KiB granularity, discarding one complete block at offset
384 KiB is split into 128 KiB and 64 KiB bios. Neither covers a complete
thin block, so dm-thin ignores both and the mapping remains allocated.
Use sector_div() to find the distance to the next granularity boundary,
and rounddown() to align the maximum bio size. This handles non-power-of-
two granularities while preserving the alignment for power-of-two ones.
When discard is unsupported or disabled, discard_granularity can be zero.
Return BIO_MAX_SECTORS in that case so the existing bio submission checks
can handle unsupported discard requests without dividing by zero.
Fixes: 9b15d109a6b2 ("block: improve discard bio alignment in
__blkdev_issue_discard()")
Reported-by: Ming-Hung Tsai <[email protected]>
Link:
https://lore.kernel.org/r/CALjSBEvjbiGDVewuapWKhGDtaxZwcn4=22rauibeoyj22ry...@mail.gmail.com
Cc: [email protected]
Signed-off-by: Hungyu Lin <[email protected]>
---
Changes in v2:
- Handle zero discard_granularity before dividing, as pointed out by
Sashiko. Leave unsupported discard handling to the bio submission path.
block/blk-lib.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/block/blk-lib.c b/block/blk-lib.c
index 688bc67cbf73..5649e4d3b5bf 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -13,26 +13,28 @@
static sector_t bio_discard_limit(struct block_device *bdev, sector_t sector)
{
unsigned int discard_granularity = bdev_discard_granularity(bdev);
- sector_t granularity_aligned_sector;
+ unsigned int remainder;
+
+ if (!discard_granularity)
+ return BIO_MAX_SECTORS;
if (bdev_is_partition(bdev))
sector += bdev->bd_start_sect;
- granularity_aligned_sector =
- round_up(sector, discard_granularity >> SECTOR_SHIFT);
+ remainder = sector_div(sector, discard_granularity >> SECTOR_SHIFT);
/*
* Make sure subsequent bios start aligned to the discard granularity if
* it needs to be split.
*/
- if (granularity_aligned_sector != sector)
- return granularity_aligned_sector - sector;
+ if (remainder)
+ return (discard_granularity >> SECTOR_SHIFT) - remainder;
/*
* 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(BIO_MAX_SIZE, discard_granularity) >> SECTOR_SHIFT;
+ return rounddown(BIO_MAX_SIZE, discard_granularity) >> SECTOR_SHIFT;
}
struct bio *blk_alloc_discard_bio(struct block_device *bdev,
--
2.43.0
