diff options
Diffstat (limited to 'block-qcow2.c')
| -rw-r--r-- | block-qcow2.c | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/block-qcow2.c b/block-qcow2.c index 74a0dfa156..a984611a9a 100644 --- a/block-qcow2.c +++ b/block-qcow2.c @@ -903,6 +903,12 @@ 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]; @@ -916,7 +922,8 @@ 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: |