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-rw-r--r--block/qcow2-refcount.c11
1 files changed, 9 insertions, 2 deletions
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 5ebbcb63d..fa78e46ee 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -215,8 +215,6 @@ static int64_t alloc_refcount_block(BlockDriverState *bs, int64_t cluster_index)
/* Allocate the refcount block itself and mark it as used */
uint64_t new_block = alloc_clusters_noref(bs, s->cluster_size);
- memset(s->refcount_block_cache, 0, s->cluster_size);
- s->refcount_block_cache_offset = new_block;
#ifdef DEBUG_ALLOC2
fprintf(stderr, "qcow2: Allocate refcount block %d for %" PRIx64
@@ -225,6 +223,10 @@ static int64_t alloc_refcount_block(BlockDriverState *bs, int64_t cluster_index)
#endif
if (in_same_refcount_block(s, new_block, cluster_index << s->cluster_bits)) {
+ /* Zero the new refcount block before updating it */
+ memset(s->refcount_block_cache, 0, s->cluster_size);
+ s->refcount_block_cache_offset = new_block;
+
/* The block describes itself, need to update the cache */
int block_index = (new_block >> s->cluster_bits) &
((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
@@ -236,6 +238,11 @@ static int64_t alloc_refcount_block(BlockDriverState *bs, int64_t cluster_index)
if (ret < 0) {
goto fail_block;
}
+
+ /* Initialize the new refcount block only after updating its refcount,
+ * update_refcount uses the refcount cache itself */
+ memset(s->refcount_block_cache, 0, s->cluster_size);
+ s->refcount_block_cache_offset = new_block;
}
/* Now the new refcount block needs to be written to disk */