block: fix alignment_offset math that assumes io_min is a power-of-2

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@redhat.com>
Cc: stable@vger.kernel.org
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 038b40f84c7a..554639249fd6 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1279,10 +1279,9 @@ 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)