[PATCH 3.16.y-ckt 112/254] block: fix alignment_offset math that assumes io_min is a power-of-2

From: Luis Henriques
Date: Tue Nov 25 2014 - 06:29:14 EST


3.16.7-ckt2 -stable review patch. If anyone has any objections, please let me know.

------------------

From: Mike Snitzer <snitzer@xxxxxxxxxx>

commit b8839b8c55f3fdd60dc36abcda7e0266aff7985c upstream.

The math in both blk_stack_limits() and queue_limit_alignment_offset()
assume that a block device's io_min (aka minimum_io_size) is always a
power-of-2. Fix the math such that it works for non-power-of-2 io_min.

This issue (of alignment_offset != 0) became apparent when testing
dm-thinp with a thinp blocksize that matches a RAID6 stripesize of
1280K. Commit fdfb4c8c1 ("dm thin: set minimum_io_size to pool's data
block size") unlocked the potential for alignment_offset != 0 due to
the dm-thin-pool's io_min possibly being a non-power-of-2.

Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Acked-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
block/blk-settings.c | 4 ++--
include/linux/blkdev.h | 5 ++---
2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index f1a1795a5683..aa02247d227e 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -574,7 +574,7 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
bottom = max(b->physical_block_size, b->io_min) + alignment;

/* Verify that top and bottom intervals line up */
- if (max(top, bottom) & (min(top, bottom) - 1)) {
+ if (max(top, bottom) % min(top, bottom)) {
t->misaligned = 1;
ret = -1;
}
@@ -619,7 +619,7 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,

/* Find lowest common alignment_offset */
t->alignment_offset = lcm(t->alignment_offset, alignment)
- & (max(t->physical_block_size, t->io_min) - 1);
+ % max(t->physical_block_size, t->io_min);

/* Verify that new alignment_offset is on a logical block boundary */
if (t->alignment_offset & (t->logical_block_size - 1)) {
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 279390ee523a..4b92fcb7e0e1 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1282,10 +1282,9 @@ static inline int queue_alignment_offset(struct request_queue *q)
static inline int queue_limit_alignment_offset(struct queue_limits *lim, sector_t sector)
{
unsigned int granularity = max(lim->physical_block_size, lim->io_min);
- unsigned int alignment = (sector << 9) & (granularity - 1);
+ unsigned int alignment = sector_div(sector, granularity >> 9) << 9;

- return (granularity + lim->alignment_offset - alignment)
- & (granularity - 1);
+ return (granularity + lim->alignment_offset - alignment) % granularity;
}

static inline int bdev_alignment_offset(struct block_device *bdev)
--
2.1.0

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