From: Mike Snitzer <snitzer@redhat.com>
Date: Wed, 8 Oct 2014 22:26:13 +0000 (-0400)
Subject: block: fix alignment_offset math that assumes io_min is a power-of-2
X-Git-Tag: v3.2.65~113
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5c250851e1f7850dfe765ff8f6d04ef4ce6e19a7;p=pandora-kernel.git

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

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@redhat.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

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