From 58cb4d8c3c6701294fc4dabec19229358d7fbc80 Mon Sep 17 00:00:00 2001
From: Gleb Natapov <gleb@redhat.com>
Date: Sun, 10 May 2009 16:03:52 +0300
Subject: [PATCH 05/16] Fix cluster freeing in qcow2

Upstream commit d4d698f020e50333d6eae48ce323752613b5c3ea
BZ: 500051

Need to drop QCOW_OFLAG_COPIED from a cluster pointer before freeing it.
Add an explanation how thing meant to work.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Bugzilla: 501729
Message-ID: <20090510130352.GF18554@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Andrea Arcangeli <aarcange@redhat.com>
RH-Upstream-status: applied(kvm/master)
Acked-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Dor Laor <dlaor@redhat.com>
---
 qemu/block-qcow2.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/qemu/block-qcow2.c b/qemu/block-qcow2.c
index 8ec2d87..a8e9e8e 100644
--- a/qemu/block-qcow2.c
+++ b/qemu/block-qcow2.c
@@ -1020,6 +1020,12 @@ static int alloc_cluster_link_l2(BlockDriverState *bs, uint64_t cluster_offset,
         goto err;
 
     for (i = 0; i < m->nb_clusters; i++) {
+        /* if two concurrent writes happen to the same unallocated cluster
+	 * each write allocates separate cluster and writes data concurrently.
+	 * The first one to complete updates l2 table with pointer to its
+	 * cluster the second one has to do RMW (which is done above by
+	 * copy_sectors()), update l2 table with its cluster pointer and free
+	 * old cluster. This is what this loop does */
         if(l2_table[l2_index + i] != 0)
             old_cluster[j++] = l2_table[l2_index + i];
 
@@ -1033,7 +1039,8 @@ static int alloc_cluster_link_l2(BlockDriverState *bs, uint64_t cluster_offset,
         goto err;
 
     for (i = 0; i < j; i++)
-        free_any_clusters(bs, be64_to_cpu(old_cluster[i]), 1);
+        free_any_clusters(bs, be64_to_cpu(old_cluster[i]) & ~QCOW_OFLAG_COPIED,
+                          1);
 
     ret = 0;
 err:
-- 
1.6.3.rc4.29.g8146