When copying L2 tables (this happens only with internal snapshots), the order
wasn't completely safe, so that after a crash you could end up with a L2 table
that has too low refcount, possibly leading to corruption in the long run.
This patch puts the operations in the right order: First allocate the new
L2 table and replace the reference, and only then decrease the refcount of the
old table.
Signed-off-by: Kevin Wolf <kw...@redhat.com>
(cherry picked from commit 16fde5f2c2788232b16c06d34d0459a5c1ec1f6c)
---
block/qcow2-cluster.c | 9 ++++++---
1 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 437aaa8..750abe3 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -515,13 +515,16 @@ static int get_cluster_table(BlockDriverState *bs,
uint64_t offset,
return ret;
}
} else {
- /* FIXME Order */
- if (l2_offset)
- qcow2_free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t));
+ /* First allocate a new L2 table (and do COW if needed) */
ret = l2_allocate(bs, l1_index, &l2_table);
if (ret < 0) {
return ret;
}
+
+ /* Then decrease the refcount of the old table */
+ if (l2_offset) {
+ qcow2_free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t));
+ }
l2_offset = s->l1_table[l1_index] & ~QCOW_OFLAG_COPIED;
}
--
1.7.2.3
