From fb80eeb70d053e927a4c801bffd22b68eb840e12 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@redhat.com>
Date: Thu, 10 Dec 2009 23:52:22 +0000
Subject: [PATCH] --- yaml --- r: 176557 b: refs/heads/master c:
 12fc0f49dc994d8d90dcf3df13f5b1ee5441288d h: refs/heads/master i:   176555:
 04c3d147b9a91364b8e6ad1203c6f3e2f371ae46 v: v3

---
 [refs]                   |  2 +-
 trunk/drivers/md/dm-io.c | 10 +++++++---
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/[refs] b/[refs]
index 68afae1f4a16..f956f3b4be74 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 67a46dad25ccc8910995d8671f7ec17a6bc823cb
+refs/heads/master: 12fc0f49dc994d8d90dcf3df13f5b1ee5441288d
diff --git a/trunk/drivers/md/dm-io.c b/trunk/drivers/md/dm-io.c
index f6a714c5aab0..10f457ca6af2 100644
--- a/trunk/drivers/md/dm-io.c
+++ b/trunk/drivers/md/dm-io.c
@@ -309,7 +309,11 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
 	unsigned num_bvecs;
 	sector_t remaining = where->count;
 
-	while (remaining) {
+	/*
+	 * where->count may be zero if rw holds a write barrier and we
+	 * need to send a zero-sized barrier.
+	 */
+	do {
 		/*
 		 * Allocate a suitably sized-bio.
 		 */
@@ -339,7 +343,7 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
 
 		atomic_inc(&io->count);
 		submit_bio(rw, bio);
-	}
+	} while (remaining);
 }
 
 static void dispatch_io(int rw, unsigned int num_regions,
@@ -360,7 +364,7 @@ static void dispatch_io(int rw, unsigned int num_regions,
 	 */
 	for (i = 0; i < num_regions; i++) {
 		*dp = old_pages;
-		if (where[i].count)
+		if (where[i].count || (rw & (1 << BIO_RW_BARRIER)))
 			do_region(rw, i, where + i, dp, io);
 	}