From: Mikulas Patocka <mpatocka@redhat.com>
Date: Wed, 2 Dec 2009 05:09:30 -0500
Subject: [md] fix data corruption with different chunksizes
Message-id: <Pine.LNX.4.64.0912020006560.11782@hs20-bc2-1.build.redhat.com>
Patchwork-id: 21641
O-Subject: [RHEL5.5 PATCH] bz210490: fix data corruption with different
	chunksizes
Bugzilla: 210490
RH-Acked-by: Jonathan E Brassow <jbrassow@redhat.com>

Hi

This patch fixes data corruption with multiple snapshots with different
chunksizes. The patch is simple, it just sorts snapshots according to the
chunk size.

Upstream status: in 2.6.32-rc6, 6d45d93ead319423099b82a4efd775bc0f159121

Testing: the race is non-reproducible, so I ran only a simple test
involving multiple snapshots to make sure that it didn't break anything.


diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 1d240dd..0c58db2 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -228,6 +228,7 @@ static void __insert_origin(struct origin *o)
  */
 static int register_snapshot(struct dm_snapshot *snap)
 {
+	struct dm_snapshot *l;
 	struct origin *o;
 	struct block_device *bdev = snap->origin->bdev;
 
@@ -249,7 +250,11 @@ static int register_snapshot(struct dm_snapshot *snap)
 		__insert_origin(o);
 	}
 
-	list_add_tail(&snap->list, &o->snapshots);
+	/* Sort the list according to chunk size, largest-first smallest-last */
+	list_for_each_entry(l, &o->snapshots, list)
+		if (l->chunk_size < snap->chunk_size)
+			break;
+	list_add_tail(&snap->list, &l->list);
 
 	up_write(&_origins_lock);
 	return 0;