In the case of a race condition between two writes a l2 entry can be written
without QCOW_OFLAG_COPIED before the first write fill it.
This patch simply check if the l2 entry has the correct offset without
QCOW_OFLAG_COPIED and do nothing.
Signed-off-by: Benoit Canet <ben...@irqsave.net>
---
block/qcow2-cluster.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index dbcb6d2..07037a0 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -709,6 +709,10 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs,
QCowL2Meta *m)
qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);
for (i = 0; i < m->nb_clusters; i++) {
+ if (be64_to_cpu(l2_table[l2_index + i]) ==
+ (cluster_offset + (i << s->cluster_bits))) {
+ continue;
+ }
/* 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
--
1.7.10.4
