Re: [dpdk-dev] [PATCH v4 03/29] graph: implement node operations

[Andrzej Ostruszka <amo@semihalf.com>]

On 4/5/20 10:55 AM, jerinj@marvell.com wrote:
[...]
> diff --git a/lib/librte_graph/node.c b/lib/librte_graph/node.c
> index 336cd1c94..d04a0fce0 100644
> --- a/lib/librte_graph/node.c
> +++ b/lib/librte_graph/node.c
[...]
> +static rte_edge_t
> +edge_update(struct node *node, struct node *prev, rte_edge_t from,
> +	    const char **next_nodes, rte_edge_t nb_edges)
> +{
> +	rte_edge_t i, max_edges, count = 0;
> +	struct node *new_node;
> +	bool need_realloc;
> +	size_t sz;
> +
> +	if (from == RTE_EDGE_ID_INVALID)
> +		from = node->nb_edges;
> +
> +	/* Don't create hole in next_nodes[] list */
> +	if (from > node->nb_edges) {
> +		rte_errno = ENOMEM;
> +		goto fail;
> +	}
> +
> +	/* Remove me from list */
> +	STAILQ_REMOVE(&node_list, node, node, next);
> +
> +	/* Allocate the storage space for new node if required */
> +	max_edges = from + nb_edges;
> +	need_realloc = max_edges > node->nb_edges;
> +	if (need_realloc) {
> +		sz = sizeof(struct node) + (max_edges * RTE_NODE_NAMESIZE);
> +		new_node = realloc(node, sz);
> +		if (new_node == NULL) {
> +			rte_errno = ENOMEM;
> +			goto restore;
> +		} else {
> +			node = new_node;
> +		}
> +	}
> +
> +	/* Update the new nodes name */
> +	for (i = from; i < max_edges; i++, count++) {
> +		if (rte_strscpy(node->next_nodes[i], next_nodes[count],
> +				RTE_NODE_NAMESIZE) < 0) {
> +			rte_errno = E2BIG;
> +			goto restore;
> +		}
> +	}
> +restore:
> +	/* Update the linked list to point new node address in prev node */
> +	if (prev)
> +		STAILQ_INSERT_AFTER(&node_list, prev, node, next);
> +	else
> +		STAILQ_INSERT_HEAD(&node_list, node, next);

AFAIU node_list keeps the list of nodes - so I guess you wanted here
"replace" the old node pointer with the new one.  I have not yet seen
the usage of this function but it seems to me like you unconditionally
insert the updated node - possibly having node pointer present doubly or
with stale pointer.  I might be missing something here.

> +
> +	if (need_realloc)
> +		node->nb_edges += max_edges;

It looks to me like this should be simple '='.

> +
> +fail:
> +	return count;
> +}
[...]
> +rte_edge_t
> +rte_node_edge_update(rte_node_t id, rte_edge_t from, const char **next_nodes,
> +		     uint16_t nb_edges)
> +{
> +	rte_edge_t rc = RTE_EDGE_ID_INVALID;
> +	struct node *n, *prev;
> +
> +	NODE_ID_CHECK(id);
> +	graph_spinlock_lock();
> +
> +	prev = NULL;
> +	STAILQ_FOREACH(n, &node_list, next) {
> +		if (n->id == id) {
> +			rc = edge_update(n, prev, from, next_nodes, nb_edges);
> +			break;
> +		}
> +		prev = n;
> +	}

OK so in this context my comment above seems to be valid.  When we find
the id we have: prev -> n, we call update() and in there we insert
new_node after prev so we end up with: prev -> n' -> n where n' might be
new address for n or just n when no realloc was performed.

Do I miss anything?

> +
> +	graph_spinlock_unlock();
> +fail:
> +	return rc;
> +}
> +
> +static rte_node_t
> +node_copy_edges(struct node *node, char *next_nodes[])
> +{
> +	rte_edge_t i;
> +
> +	for (i = 0; i < node->nb_edges; i++)
> +		next_nodes[i] = node->next_nodes[i];
> +
> +	return i;
> +}
> +
> +rte_node_t
> +rte_node_edge_get(rte_node_t id, char *next_nodes[])
> +{
> +	rte_node_t rc = RTE_NODE_ID_INVALID;
> +	struct node *node;
> +
> +	NODE_ID_CHECK(id);
> +	graph_spinlock_lock();
> +
> +	STAILQ_FOREACH(node, &node_list, next) {
> +		if (node->id == id) {
> +			if (next_nodes == NULL)
> +				rc = sizeof(char *) * node->nb_edges;
> +			else
> +				rc = node_copy_edges(node, next_nodes);

Do we want to ready for next_nodes not large enough?

> +			break;
> +		}
> +	}
> +
> +	graph_spinlock_unlock();
> +fail:
> +	return rc;
> +}

[...]

With regards
Andrzej Ostruszka