From: Cosmin Ratiu <cratiu@nvidia.com>

Upcoming changes to the rate commands need the parent devlink specified.
This change adds a nested 'parent-dev' attribute to the API and helpers
to obtain and put a reference to the parent devlink instance in
info->user_ptr[1].

To avoid deadlocks, the parent devlink is unlocked before obtaining the
main devlink instance that is the target of the request.
A reference to the parent is kept until the end of the request to avoid
it suddenly disappearing.

This means that this reference is of limited use without additional
protection.

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>
---
 Documentation/netlink/specs/devlink.yaml | 11 ++++
 include/uapi/linux/devlink.h             |  2 +
 net/devlink/devl_internal.h              |  2 +
 net/devlink/netlink.c                    | 67 ++++++++++++++++++++++--
 net/devlink/netlink_gen.c                |  5 ++
 net/devlink/netlink_gen.h                |  8 +++
 6 files changed, 90 insertions(+), 5 deletions(-)

diff --git a/Documentation/netlink/specs/devlink.yaml b/Documentation/netlink/specs/devlink.yaml
index 837112da6738..1f41d934dc5b 100644
--- a/Documentation/netlink/specs/devlink.yaml
+++ b/Documentation/netlink/specs/devlink.yaml
@@ -867,6 +867,9 @@ attribute-sets:
         type: flag
         doc: Request restoring parameter to its default value.
         value: 183
+      - name: parent-dev
+        type: nest
+        nested-attributes: dl-parent-dev
   -
     name: dl-dev-stats
     subset-of: devlink
@@ -1289,6 +1292,14 @@ attribute-sets:
              Specifies the bandwidth share assigned to the Traffic Class.
              The bandwidth for the traffic class is determined
              in proportion to the sum of the shares of all configured classes.
+  -
+    name: dl-parent-dev
+    subset-of: devlink
+    attributes:
+      -
+        name: bus-name
+      -
+        name: dev-name
 
 operations:
   enum-model: directional
diff --git a/include/uapi/linux/devlink.h b/include/uapi/linux/devlink.h
index e7d6b6d13470..94b8a4437bac 100644
--- a/include/uapi/linux/devlink.h
+++ b/include/uapi/linux/devlink.h
@@ -642,6 +642,8 @@ enum devlink_attr {
 	DEVLINK_ATTR_PARAM_VALUE_DEFAULT,	/* dynamic */
 	DEVLINK_ATTR_PARAM_RESET_DEFAULT,	/* flag */
 
+	DEVLINK_ATTR_PARENT_DEV,		/* nested */
+
 	/* Add new attributes above here, update the spec in
 	 * Documentation/netlink/specs/devlink.yaml and re-generate
 	 * net/devlink/netlink_gen.c.
diff --git a/net/devlink/devl_internal.h b/net/devlink/devl_internal.h
index 8374c9cab6ce..3ca4cc8517cd 100644
--- a/net/devlink/devl_internal.h
+++ b/net/devlink/devl_internal.h
@@ -162,6 +162,8 @@ typedef int devlink_nl_dump_one_func_t(struct sk_buff *msg,
 struct devlink *
 devlink_get_from_attrs_lock(struct net *net, struct nlattr **attrs,
 			    bool dev_lock);
+struct devlink *
+devlink_get_parent_from_attrs_lock(struct net *net, struct nlattr **attrs);
 
 int devlink_nl_dumpit(struct sk_buff *msg, struct netlink_callback *cb,
 		      devlink_nl_dump_one_func_t *dump_one);
diff --git a/net/devlink/netlink.c b/net/devlink/netlink.c
index 593605c1b1ef..781758b8632c 100644
--- a/net/devlink/netlink.c
+++ b/net/devlink/netlink.c
@@ -12,6 +12,7 @@
 #define DEVLINK_NL_FLAG_NEED_PORT		BIT(0)
 #define DEVLINK_NL_FLAG_NEED_DEVLINK_OR_PORT	BIT(1)
 #define DEVLINK_NL_FLAG_NEED_DEV_LOCK		BIT(2)
+#define DEVLINK_NL_FLAG_OPTIONAL_PARENT_DEV	BIT(3)
 
 static const struct genl_multicast_group devlink_nl_mcgrps[] = {
 	[DEVLINK_MCGRP_CONFIG] = { .name = DEVLINK_GENL_MCGRP_CONFIG_NAME },
@@ -206,19 +207,51 @@ devlink_get_from_attrs_lock(struct net *net, struct nlattr **attrs,
 	return ERR_PTR(-ENODEV);
 }
 
+struct devlink *
+devlink_get_parent_from_attrs_lock(struct net *net, struct nlattr **attrs)
+{
+	struct nlattr *tb[DEVLINK_ATTR_DEV_NAME + 1];
+	int err;
+
+	if (!attrs[DEVLINK_ATTR_PARENT_DEV])
+		return ERR_PTR(-EINVAL);
+
+	err = nla_parse_nested(tb, DEVLINK_ATTR_DEV_NAME,
+			       attrs[DEVLINK_ATTR_PARENT_DEV],
+			       devlink_dl_parent_dev_nl_policy, NULL);
+	if (err)
+		return ERR_PTR(err);
+
+	return devlink_get_from_attrs_lock(net, tb, false);
+}
+
 static int __devlink_nl_pre_doit(struct sk_buff *skb, struct genl_info *info,
 				 u8 flags)
 {
+	bool parent_dev = flags & DEVLINK_NL_FLAG_OPTIONAL_PARENT_DEV;
 	bool dev_lock = flags & DEVLINK_NL_FLAG_NEED_DEV_LOCK;
+	struct devlink *devlink, *parent_devlink = NULL;
+	struct net *net = genl_info_net(info);
+	struct nlattr **attrs = info->attrs;
 	struct devlink_port *devlink_port;
-	struct devlink *devlink;
 	int err;
 
-	devlink = devlink_get_from_attrs_lock(genl_info_net(info), info->attrs,
-					      dev_lock);
-	if (IS_ERR(devlink))
-		return PTR_ERR(devlink);
+	if (parent_dev && attrs[DEVLINK_ATTR_PARENT_DEV]) {
+		parent_devlink = devlink_get_parent_from_attrs_lock(net, attrs);
+		if (IS_ERR(parent_devlink))
+			return PTR_ERR(parent_devlink);
+		info->user_ptr[1] = parent_devlink;
+		/* Drop the parent devlink lock but don't release the reference.
+		 * This will keep it alive until the end of the request.
+		 */
+		devl_unlock(parent_devlink);
+	}
 
+	devlink = devlink_get_from_attrs_lock(net, attrs, dev_lock);
+	if (IS_ERR(devlink)) {
+		err = PTR_ERR(devlink);
+		goto parent_put;
+	}
 	info->user_ptr[0] = devlink;
 	if (flags & DEVLINK_NL_FLAG_NEED_PORT) {
 		devlink_port = devlink_port_get_from_info(devlink, info);
@@ -237,6 +270,9 @@ static int __devlink_nl_pre_doit(struct sk_buff *skb, struct genl_info *info,
 unlock:
 	devl_dev_unlock(devlink, dev_lock);
 	devlink_put(devlink);
+parent_put:
+	if (parent_dev && parent_devlink)
+		devlink_put(parent_devlink);
 	return err;
 }
 
@@ -265,6 +301,14 @@ int devlink_nl_pre_doit_port_optional(const struct genl_split_ops *ops,
 	return __devlink_nl_pre_doit(skb, info, DEVLINK_NL_FLAG_NEED_DEVLINK_OR_PORT);
 }
 
+int devlink_nl_pre_doit_parent_dev_optional(const struct genl_split_ops *ops,
+					    struct sk_buff *skb,
+					    struct genl_info *info)
+{
+	return __devlink_nl_pre_doit(skb, info,
+				     DEVLINK_NL_FLAG_OPTIONAL_PARENT_DEV);
+}
+
 static void __devlink_nl_post_doit(struct sk_buff *skb, struct genl_info *info,
 				   u8 flags)
 {
@@ -274,6 +318,11 @@ static void __devlink_nl_post_doit(struct sk_buff *skb, struct genl_info *info,
 	devlink = info->user_ptr[0];
 	devl_dev_unlock(devlink, dev_lock);
 	devlink_put(devlink);
+	if ((flags & DEVLINK_NL_FLAG_OPTIONAL_PARENT_DEV) &&
+	    info->user_ptr[1]) {
+		devlink = info->user_ptr[1];
+		devlink_put(devlink);
+	}
 }
 
 void devlink_nl_post_doit(const struct genl_split_ops *ops,
@@ -289,6 +338,14 @@ devlink_nl_post_doit_dev_lock(const struct genl_split_ops *ops,
 	__devlink_nl_post_doit(skb, info, DEVLINK_NL_FLAG_NEED_DEV_LOCK);
 }
 
+void
+devlink_nl_post_doit_parent_dev_optional(const struct genl_split_ops *ops,
+					 struct sk_buff *skb,
+					 struct genl_info *info)
+{
+	__devlink_nl_post_doit(skb, info, DEVLINK_NL_FLAG_OPTIONAL_PARENT_DEV);
+}
+
 static int devlink_nl_inst_single_dumpit(struct sk_buff *msg,
 					 struct netlink_callback *cb, int flags,
 					 devlink_nl_dump_one_func_t *dump_one,
diff --git a/net/devlink/netlink_gen.c b/net/devlink/netlink_gen.c
index 580985025f49..8fbe0417ab55 100644
--- a/net/devlink/netlink_gen.c
+++ b/net/devlink/netlink_gen.c
@@ -38,6 +38,11 @@ devlink_attr_param_type_validate(const struct nlattr *attr,
 }
 
 /* Common nested types */
+const struct nla_policy devlink_dl_parent_dev_nl_policy[DEVLINK_ATTR_DEV_NAME + 1] = {
+	[DEVLINK_ATTR_BUS_NAME] = { .type = NLA_NUL_STRING, },
+	[DEVLINK_ATTR_DEV_NAME] = { .type = NLA_NUL_STRING, },
+};
+
 const struct nla_policy devlink_dl_port_function_nl_policy[DEVLINK_PORT_FN_ATTR_CAPS + 1] = {
 	[DEVLINK_PORT_FUNCTION_ATTR_HW_ADDR] = { .type = NLA_BINARY, },
 	[DEVLINK_PORT_FN_ATTR_STATE] = NLA_POLICY_MAX(NLA_U8, 1),
diff --git a/net/devlink/netlink_gen.h b/net/devlink/netlink_gen.h
index 09cc6f264ccf..94566cab1734 100644
--- a/net/devlink/netlink_gen.h
+++ b/net/devlink/netlink_gen.h
@@ -12,6 +12,7 @@
 #include <uapi/linux/devlink.h>
 
 /* Common nested types */
+extern const struct nla_policy devlink_dl_parent_dev_nl_policy[DEVLINK_ATTR_DEV_NAME + 1];
 extern const struct nla_policy devlink_dl_port_function_nl_policy[DEVLINK_PORT_FN_ATTR_CAPS + 1];
 extern const struct nla_policy devlink_dl_rate_tc_bws_nl_policy[DEVLINK_RATE_TC_ATTR_BW + 1];
 extern const struct nla_policy devlink_dl_selftest_id_nl_policy[DEVLINK_ATTR_SELFTEST_ID_FLASH + 1];
@@ -28,12 +29,19 @@ int devlink_nl_pre_doit_dev_lock(const struct genl_split_ops *ops,
 int devlink_nl_pre_doit_port_optional(const struct genl_split_ops *ops,
 				      struct sk_buff *skb,
 				      struct genl_info *info);
+int devlink_nl_pre_doit_parent_dev_optional(const struct genl_split_ops *ops,
+					    struct sk_buff *skb,
+					    struct genl_info *info);
 void
 devlink_nl_post_doit(const struct genl_split_ops *ops, struct sk_buff *skb,
 		     struct genl_info *info);
 void
 devlink_nl_post_doit_dev_lock(const struct genl_split_ops *ops,
 			      struct sk_buff *skb, struct genl_info *info);
+void
+devlink_nl_post_doit_parent_dev_optional(const struct genl_split_ops *ops,
+					 struct sk_buff *skb,
+					 struct genl_info *info);
 
 int devlink_nl_get_doit(struct sk_buff *skb, struct genl_info *info);
 int devlink_nl_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb);
-- 
2.31.1

On Tue, Nov 25, 2025 at 10:06:05PM +0200, Tariq Toukan wrote:
> From: Cosmin Ratiu <cratiu@nvidia.com>
> 
> Upcoming changes to the rate commands need the parent devlink specified.
> This change adds a nested 'parent-dev' attribute to the API and helpers
> to obtain and put a reference to the parent devlink instance in
> info->user_ptr[1].
> 
> To avoid deadlocks, the parent devlink is unlocked before obtaining the
> main devlink instance that is the target of the request.
> A reference to the parent is kept until the end of the request to avoid
> it suddenly disappearing.
> 
> This means that this reference is of limited use without additional
> protection.
> 
> 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>
> ---
>  Documentation/netlink/specs/devlink.yaml | 11 ++++
>  include/uapi/linux/devlink.h             |  2 +
>  net/devlink/devl_internal.h              |  2 +
>  net/devlink/netlink.c                    | 67 ++++++++++++++++++++++--
>  net/devlink/netlink_gen.c                |  5 ++
>  net/devlink/netlink_gen.h                |  8 +++

Hi,

I think that the updates to netlink_gen.[ch] belong in
the following patch rather than this one.

You can observe this using

tools/net/ynl/ynl-regen.sh -f && git diff

On Thu, 2025-11-27 at 15:28 +0000, Simon Horman wrote:
> On Tue, Nov 25, 2025 at 10:06:05PM +0200, Tariq Toukan wrote:
> >  net/devlink/netlink_gen.c                |  5 ++
> >  net/devlink/netlink_gen.h                |  8 +++
> 
> Hi,
> 
> I think that the updates to netlink_gen.[ch] belong in
> the following patch rather than this one.
> 
> You can observe this using
> 
> tools/net/ynl/ynl-regen.sh -f && git diff

Hi,

You are right, some of these changes belong to the next patch. We will
fix in the next submission.
But running ynl-regen.sh results in unbuildable code, due to missing
devlink_dl_parent_dev_nl_policy. It seems it is not added unless the
attribute is referenced in at least one attribute set.
Additionally, the devlink_nl_pre_doit_parent_dev_optional needs to be
manually added to netlink-gen.{h,c}, as it is not automatically
generated.

Cosmin.