From 6b42f1b153e34d8e2023f54623fb8830d1cb9851 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 19 Dec 2012 07:18:35 -0800
Subject: [PATCH] --- yaml --- r: 347087 b: refs/heads/master c:
 59771079c18c44e39106f0f30054025acafadb41 h: refs/heads/master i:   347085:
 3aa68b813bbf1cfa7566f7bb41d961ba66da73c7   347083:
 fcdf68a38bb6e50e62b6de422734b88a28110e3e   347079:
 f816fccd598dfc32dd680a69a9a3391869792559   347071:
 d2e2e6deb94ed046439d27bcefb65b47f0e0d6b8 v: v3

---
 [refs]                       |  2 +-
 trunk/include/linux/blkdev.h | 19 +++++++++++++++----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/[refs] b/[refs]
index 54c1240e7e04..724d31067d02 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 752451f01c4567b506bf4343082682dbb8fb30dd
+refs/heads/master: 59771079c18c44e39106f0f30054025acafadb41
diff --git a/trunk/include/linux/blkdev.h b/trunk/include/linux/blkdev.h
index acb4f7bbbd32..f94bc83011ed 100644
--- a/trunk/include/linux/blkdev.h
+++ b/trunk/include/linux/blkdev.h
@@ -1188,14 +1188,25 @@ static inline int queue_discard_alignment(struct request_queue *q)
 
 static inline int queue_limit_discard_alignment(struct queue_limits *lim, sector_t sector)
 {
-	sector_t alignment = sector << 9;
-	alignment = sector_div(alignment, lim->discard_granularity);
+	unsigned int alignment, granularity, offset;
 
 	if (!lim->max_discard_sectors)
 		return 0;
 
-	alignment = lim->discard_granularity + lim->discard_alignment - alignment;
-	return sector_div(alignment, lim->discard_granularity);
+	/* Why are these in bytes, not sectors? */
+	alignment = lim->discard_alignment >> 9;
+	granularity = lim->discard_granularity >> 9;
+	if (!granularity)
+		return 0;
+
+	/* Offset of the partition start in 'granularity' sectors */
+	offset = sector_div(sector, granularity);
+
+	/* And why do we do this modulus *again* in blkdev_issue_discard()? */
+	offset = (granularity + alignment - offset) % granularity;
+
+	/* Turn it back into bytes, gaah */
+	return offset << 9;
 }
 
 static inline int bdev_discard_alignment(struct block_device *bdev)