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Lunev" , Anton Nefedov , den@virtuozzo.com, mreitz@redhat.com Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" Signed-off-by: Anton Nefedov Signed-off-by: Denis V. Lunev --- block/qcow2-cluster.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 25210cd..4204db9 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -827,12 +827,10 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m) assert(l2_index + m->nb_clusters <= s->l2_size); 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 - * perform_cow()), update l2 table with its cluster pointer and free - * old cluster. This is what this loop does */ + /* handle_dependencies() protects from normal cluster allocation + * collision; still L2 entry might be !0 in case of zero or compressed + * cluster reusage or writing over the snapshot + */ if (l2_table[l2_index + i] != 0) { old_cluster[j++] = l2_table[l2_index + i]; }