Actually it does not cause problems but this code order seems a bit
wrong to me (block/qcow2-cluster.c)
QLIST_INSERT_HEAD(&s->cluster_allocs, m, next_in_flight);
/* allocate a new cluster */
cluster_offset = qcow2_alloc_clusters(bs, nb_clusters * s->cluster_size);
if (cluster_offset < 0) {
ret = cluster_offset;
goto fail;
}
/* save info needed for meta data update */
m->offset = offset;
m->n_start = n_start;
m->nb_clusters = nb_clusters;
current metadata (m) get inserted in cluster allocation list with
nb_clusters set to 0. Loop on cluster_allocs "ignore" (wait for this
allocation or just skip it depending on dirty data in offset field)
this metadata. Currently all occur in a CoMutex so this does not cause
problems but in case qcow2_alloc_clusters unlock the mutex it can
occur to insert two overlapping updates into cluster_allocs. Perhaps a
better order would be
/* save info needed for meta data update */
m->offset = offset;
m->n_start = n_start;
m->nb_clusters = nb_clusters;
QLIST_INSERT_HEAD(&s->cluster_allocs, m, next_in_flight);
/* allocate a new cluster */
cluster_offset = qcow2_alloc_clusters(bs, nb_clusters * s->cluster_size);
if (cluster_offset < 0) {
ret = cluster_offset;
goto fail;
}
(tested successfully with iotests suite)
Frediano
