devlink: Allow rate node parents from other devlinks

This commit makes use of the building blocks previously added to
implement cross-device rate nodes.

A new 'supported_cross_device_rate_nodes' bool is added to devlink_ops
which lets drivers advertise support for cross-device rate objects.
If enabled and if there is a common shared devlink instance, then:
- all rate objects will be stored in the top-most common nested instance
  and
- rate objects can have parents from other devices sharing the same
  common instance.

Storing rates in the common shared ancestor is safe, because it is
reference counted by its nested devlink instances, so it's guaranteed to
outlive them. Furthermore, the shared devlink infra guarantees a given
nested devlink hierarchy is managed by the same driver.

The parent devlink from info->ctx is not locked, so none of its mutable
fields can be used. But parent setting only requires comparing devlink
pointer comparisons. Additionally, since the shared devlink is locked,
other rate operations cannot concurrently happen.

Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
Reviewed-by: Carolina Jubran <cjubran@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260701073254.754518-8-tariqt@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

2 files changed, 81 insertions, 9 deletions

diff --git a/net/devlink/core.c b/net/devlink/core.c
index ee26c50b4118..c53a42e17a58 100644
--- a/net/devlink/core.c
+++ b/net/devlink/core.c
@@ -534,6 +534,9 @@ void devlink_free(struct devlink *devlink)
 {
 	ASSERT_DEVLINK_NOT_REGISTERED(devlink);
 
+	devl_lock(devlink);
+	WARN_ON(devlink_rates_check(devlink, NULL, NULL));
+	devl_unlock(devlink);
 	devlink_rel_put(devlink);
 
 	WARN_ON(!list_empty(&devlink->trap_policer_list));
@@ -544,7 +547,6 @@ void devlink_free(struct devlink *devlink)
 	WARN_ON(!list_empty(&devlink->resource_list));
 	WARN_ON(!list_empty(&devlink->dpipe_table_list));
 	WARN_ON(!list_empty(&devlink->sb_list));
-	WARN_ON(devlink_rates_check(devlink, NULL, NULL));
 	WARN_ON(!list_empty(&devlink->linecard_list));
 	WARN_ON(!xa_empty(&devlink->ports));
 
diff --git a/net/devlink/rate.c b/net/devlink/rate.c
index 78a59d79c2ea..e727c8b8b33e 100644
--- a/net/devlink/rate.c
+++ b/net/devlink/rate.c
@@ -30,14 +30,42 @@ devlink_rate_leaf_get_from_info(struct devlink *devlink, struct genl_info *info)
 	return devlink_rate ?: ERR_PTR(-ENODEV);
 }
 
+/* Repeatedly walks the nested devlink chain while cross device rate nodes are
+ * supported and finds the topmost instance where rates should be stored.
+ * That instance is locked, referenced and returned.
+ * When cross device rate nodes aren't supported the original devlink instance
+ * is returned.
+ */
 static struct devlink *devl_rate_lock(struct devlink *devlink)
 {
-	return devlink;
+	struct devlink *rate_devlink = devlink, *parent;
+
+	devl_assert_locked(devlink);
+
+	while (rate_devlink->ops &&
+	       rate_devlink->ops->supported_cross_device_rate_nodes) {
+		parent = devlink_nested_in_get_lock(rate_devlink);
+		if (!parent)
+			break;
+		if (rate_devlink != devlink) {
+			/* Unlock intermediate instances. */
+			devl_unlock(rate_devlink);
+			devlink_put(rate_devlink);
+		}
+		rate_devlink = parent;
+	}
+	return rate_devlink;
 }
 
+/* Unlocks and puts 'rate devlink' if different than 'devlink'. */
 static void devl_rate_unlock(struct devlink *devlink,
 			     struct devlink *rate_devlink)
 {
+	if (devlink == rate_devlink)
+		return;
+
+	devl_unlock(rate_devlink);
+	devlink_put(rate_devlink);
 }
 
 static struct devlink_rate *
@@ -121,6 +149,25 @@ nla_put_failure:
 	return -EMSGSIZE;
 }
 
+static int devlink_nl_rate_parent_fill(struct sk_buff *msg,
+				       struct devlink_rate *devlink_rate)
+{
+	struct devlink_rate *parent = devlink_rate->parent;
+	struct devlink *devlink = parent->devlink;
+
+	if (nla_put_string(msg, DEVLINK_ATTR_RATE_PARENT_NODE_NAME,
+			   parent->name))
+		return -EMSGSIZE;
+
+	if (devlink != devlink_rate->devlink &&
+	    devlink_nl_put_nested_handle(msg,
+					 devlink_net(devlink_rate->devlink),
+					 devlink, DEVLINK_ATTR_PARENT_DEV))
+		return -EMSGSIZE;
+
+	return 0;
+}
+
 static int devlink_nl_rate_fill(struct sk_buff *msg,
 				struct devlink_rate *devlink_rate,
 				enum devlink_command cmd, u32 portid, u32 seq,
@@ -165,10 +212,9 @@ static int devlink_nl_rate_fill(struct sk_buff *msg,
 			devlink_rate->tx_weight))
 		goto nla_put_failure;
 
-	if (devlink_rate->parent)
-		if (nla_put_string(msg, DEVLINK_ATTR_RATE_PARENT_NODE_NAME,
-				   devlink_rate->parent->name))
-			goto nla_put_failure;
+	if (devlink_rate->parent &&
+	    devlink_nl_rate_parent_fill(msg, devlink_rate))
+		goto nla_put_failure;
 
 	if (devlink_rate_put_tc_bws(msg, devlink_rate->tc_bw))
 		goto nla_put_failure;
@@ -322,13 +368,14 @@ devlink_nl_rate_parent_node_set(struct devlink_rate *devlink_rate,
 				struct genl_info *info,
 				struct nlattr *nla_parent)
 {
-	struct devlink *devlink = devlink_rate->devlink;
+	struct devlink *devlink = devlink_rate->devlink, *parent_devlink;
 	const char *parent_name = nla_data(nla_parent);
 	const struct devlink_ops *ops = devlink->ops;
 	size_t len = strlen(parent_name);
 	struct devlink_rate *parent;
 	int err = -EOPNOTSUPP;
 
+	parent_devlink = devlink_nl_ctx(info)->parent_devlink ? : devlink;
 	parent = devlink_rate->parent;
 
 	if (parent && !len) {
@@ -346,7 +393,13 @@ devlink_nl_rate_parent_node_set(struct devlink_rate *devlink_rate,
 		refcount_dec(&parent->refcnt);
 		devlink_rate->parent = NULL;
 	} else if (len) {
-		parent = devlink_rate_node_get_by_name(rate_devlink, devlink,
+		/* parent_devlink (when different than devlink) isn't locked,
+		 * but the rate node devlink instance is, so nobody from the
+		 * same group of devices sharing rates could change the used
+		 * fields or unregister the parent.
+		 */
+		parent = devlink_rate_node_get_by_name(rate_devlink,
+						       parent_devlink,
 						       parent_name);
 		if (IS_ERR(parent))
 			return -ENODEV;
@@ -633,9 +686,11 @@ static bool devlink_rate_set_ops_supported(const struct devlink_ops *ops,
 
 int devlink_nl_rate_set_doit(struct sk_buff *skb, struct genl_info *info)
 {
-	struct devlink *rate_devlink, *devlink = devlink_nl_ctx(info)->devlink;
+	struct devlink_nl_ctx *ctx = devlink_nl_ctx(info);
+	struct devlink *devlink = ctx->devlink;
 	struct devlink_rate *devlink_rate;
 	const struct devlink_ops *ops;
+	struct devlink *rate_devlink;
 	int err;
 
 	rate_devlink = devl_rate_lock(devlink);
@@ -652,6 +707,14 @@ int devlink_nl_rate_set_doit(struct sk_buff *skb, struct genl_info *info)
 		goto unlock;
 	}
 
+	if (ctx->parent_devlink && ctx->parent_devlink != devlink &&
+	    !ops->supported_cross_device_rate_nodes) {
+		NL_SET_ERR_MSG(info->extack,
+			       "Cross-device rate parents aren't supported");
+		err = -EOPNOTSUPP;
+		goto unlock;
+	}
+
 	err = devlink_nl_rate_set(devlink_rate, rate_devlink, ops, info);
 
 	if (!err)
@@ -679,6 +742,13 @@ int devlink_nl_rate_new_doit(struct sk_buff *skb, struct genl_info *info)
 	if (!devlink_rate_set_ops_supported(ops, info, DEVLINK_RATE_TYPE_NODE))
 		return -EOPNOTSUPP;
 
+	if (ctx->parent_devlink && ctx->parent_devlink != devlink &&
+	    !ops->supported_cross_device_rate_nodes) {
+		NL_SET_ERR_MSG(info->extack,
+			       "Cross-device rate parents aren't supported");
+		return -EOPNOTSUPP;
+	}
+
 	rate_devlink = devl_rate_lock(devlink);
 	rate_node = devlink_rate_node_get_from_attrs(rate_devlink, devlink,
 						     info->attrs);