devlink: Fix excessive stack usage in rate TC bandwidth parsing

The devlink_nl_rate_tc_bw_parse function uses a large stack array for
devlink attributes, which triggers a warning about excessive stack
usage:

net/devlink/rate.c: In function 'devlink_nl_rate_tc_bw_parse':
net/devlink/rate.c:382:1: error: the frame size of 1648 bytes is larger than 1536 bytes [-Werror=frame-larger-than=]

Introduce a separate attribute set specifically for rate TC bandwidth
parsing that only contains the two attributes actually used: index
and bandwidth. This reduces the stack array from DEVLINK_ATTR_MAX
entries to just 2 entries, solving the stack usage issue.

Update devlink selftest to use the new 'index' and 'bw' attribute names
consistent with the YAML spec.

Example usage with ynl with the new spec:

./tools/net/ynl/cli.py --spec Documentation/netlink/specs/devlink.yaml \
--do rate-set --json '{
"bus-name": "pci",
"dev-name": "0000:08:00.0",
"port-index": 1,
"rate-tc-bws": [
{"index": 0, "bw": 50},
{"index": 1, "bw": 50},
{"index": 2, "bw": 0},
{"index": 3, "bw": 0},
{"index": 4, "bw": 0},
{"index": 5, "bw": 0},
{"index": 6, "bw": 0},
{"index": 7, "bw": 0}
]
}'

./tools/net/ynl/cli.py --spec Documentation/netlink/specs/devlink.yaml \
--do rate-get --json '{
"bus-name": "pci",
"dev-name": "0000:08:00.0",
"port-index": 1
}'

output for rate-get:
{'bus-name': 'pci',
'dev-name': '0000:08:00.0',
'port-index': 1,
'rate-tc-bws': [{'bw': 50, 'index': 0},
{'bw': 50, 'index': 1},
{'bw': 0, 'index': 2},
{'bw': 0, 'index': 3},
{'bw': 0, 'index': 4},
{'bw': 0, 'index': 5},
{'bw': 0, 'index': 6},
{'bw': 0, 'index': 7}],
'rate-tx-max': 0,
'rate-tx-priority': 0,
'rate-tx-share': 0,
'rate-tx-weight': 0,
'rate-type': 'leaf'}

Fixes: 566e8f108fc7 ("devlink: Extend devlink rate API with traffic classes bandwidth management")
Reported-by: Arnd Bergmann <[e-mail]>
Closes: https://lore.kernel.org/netdev/[e-mail]/
Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Suggested-by: Jakub Kicinski <[e-mail]>
Signed-off-by: Carolina Jubran <[e-mail]>
Tested-by: Carolina Jubran <[e-mail]>
Signed-off-by: Tariq Toukan <[e-mail]>
Reviewed-by: Jiri Pirko <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/netlink/specs/devlink.yaml

···
         type: nest
         multi-attr: true
         nested-attributes: dl-rate-tc-bws
-      -
-        name: rate-tc-index
-        type: u8
-        checks:
-          max: rate-tc-index-max
-      -
-        name: rate-tc-bw
-        type: u32
-        doc: |
-             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-dev-stats
     subset-of: devlink
···
         type: flag
   -
     name: dl-rate-tc-bws
-    subset-of: devlink
+    name-prefix: devlink-rate-tc-attr-
     attributes:
       -
-        name: rate-tc-index
+        name: index
+        type: u8
+        checks:
+          max: rate-tc-index-max
       -
-        name: rate-tc-bw
+        name: bw
+        type: u32
+        doc: |
+             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.
 
 operations:
   enum-model: directional

include/uapi/linux/devlink.h

···
 	DEVLINK_ATTR_REGION_DIRECT,		/* flag */
 
 	DEVLINK_ATTR_RATE_TC_BWS,		/* nested */
-	DEVLINK_ATTR_RATE_TC_INDEX,		/* u8 */
-	DEVLINK_ATTR_RATE_TC_BW,		/* u32 */
 
 	/* Add new attributes above here, update the spec in
 	 * Documentation/netlink/specs/devlink.yaml and re-generate
···
 
 	__DEVLINK_ATTR_MAX,
 	DEVLINK_ATTR_MAX = __DEVLINK_ATTR_MAX - 1
+};
+
+enum devlink_rate_tc_attr {
+	DEVLINK_RATE_TC_ATTR_UNSPEC,
+	DEVLINK_RATE_TC_ATTR_INDEX,		/* u8 */
+	DEVLINK_RATE_TC_ATTR_BW,		/* u32 */
+
+	__DEVLINK_RATE_TC_ATTR_MAX,
+	DEVLINK_RATE_TC_ATTR_MAX = __DEVLINK_RATE_TC_ATTR_MAX - 1
 };
 
 /* Mapping between internal resource described by the field and system

net/devlink/netlink_gen.c

···
 	[DEVLINK_PORT_FN_ATTR_CAPS] = NLA_POLICY_BITFIELD32(15),
 };
 
-const struct nla_policy devlink_dl_rate_tc_bws_nl_policy[DEVLINK_ATTR_RATE_TC_BW + 1] = {
-	[DEVLINK_ATTR_RATE_TC_INDEX] = NLA_POLICY_MAX(NLA_U8, DEVLINK_RATE_TC_INDEX_MAX),
-	[DEVLINK_ATTR_RATE_TC_BW] = { .type = NLA_U32, },
+const struct nla_policy devlink_dl_rate_tc_bws_nl_policy[DEVLINK_RATE_TC_ATTR_BW + 1] = {
+	[DEVLINK_RATE_TC_ATTR_INDEX] = NLA_POLICY_MAX(NLA_U8, DEVLINK_RATE_TC_INDEX_MAX),
+	[DEVLINK_RATE_TC_ATTR_BW] = { .type = NLA_U32, },
 };
 
 const struct nla_policy devlink_dl_selftest_id_nl_policy[DEVLINK_ATTR_SELFTEST_ID_FLASH + 1] = {

net/devlink/netlink_gen.h

···
 
 /* Common nested types */
 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_ATTR_RATE_TC_BW + 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];
 
 /* Ops table for devlink */

net/devlink/rate.c

···
 		if (!nla_tc_bw)
 			return -EMSGSIZE;
 
-		if (nla_put_u8(msg, DEVLINK_ATTR_RATE_TC_INDEX, i) ||
-		    nla_put_u32(msg, DEVLINK_ATTR_RATE_TC_BW, tc_bw[i]))
+		if (nla_put_u8(msg, DEVLINK_RATE_TC_ATTR_INDEX, i) ||
+		    nla_put_u32(msg, DEVLINK_RATE_TC_ATTR_BW, tc_bw[i]))
 			goto nla_put_failure;
 
 		nla_nest_end(msg, nla_tc_bw);
···
 				       unsigned long *bitmap,
 				       struct netlink_ext_ack *extack)
 {
-	struct nlattr *tb[DEVLINK_ATTR_MAX + 1];
+	struct nlattr *tb[DEVLINK_RATE_TC_ATTR_MAX + 1];
 	u8 tc_index;
 	int err;
 
-	err = nla_parse_nested(tb, DEVLINK_ATTR_MAX, parent_nest,
+	err = nla_parse_nested(tb, DEVLINK_RATE_TC_ATTR_MAX, parent_nest,
 			       devlink_dl_rate_tc_bws_nl_policy, extack);
 	if (err)
 		return err;
 
-	if (!tb[DEVLINK_ATTR_RATE_TC_INDEX]) {
+	if (!tb[DEVLINK_RATE_TC_ATTR_INDEX]) {
 		NL_SET_ERR_ATTR_MISS(extack, parent_nest,
-				     DEVLINK_ATTR_RATE_TC_INDEX);
+				     DEVLINK_RATE_TC_ATTR_INDEX);
 		return -EINVAL;
 	}
 
-	tc_index = nla_get_u8(tb[DEVLINK_ATTR_RATE_TC_INDEX]);
+	tc_index = nla_get_u8(tb[DEVLINK_RATE_TC_ATTR_INDEX]);
 
-	if (!tb[DEVLINK_ATTR_RATE_TC_BW]) {
+	if (!tb[DEVLINK_RATE_TC_ATTR_BW]) {
 		NL_SET_ERR_ATTR_MISS(extack, parent_nest,
-				     DEVLINK_ATTR_RATE_TC_BW);
+				     DEVLINK_RATE_TC_ATTR_BW);
 		return -EINVAL;
 	}
 
···
 		return -EINVAL;
 	}
 
-	tc_bw[tc_index] = nla_get_u32(tb[DEVLINK_ATTR_RATE_TC_BW]);
+	tc_bw[tc_index] = nla_get_u32(tb[DEVLINK_RATE_TC_ATTR_BW]);
 
 	return 0;
 }

tools/testing/selftests/drivers/net/hw/devlink_rate_tc_bw.py

···
             "port-index": port_index,
             "rate-tx-max": 125000000,
             "rate-tc-bws": [
-                {"rate-tc-index": 0, "rate-tc-bw": 0},
-                {"rate-tc-index": 1, "rate-tc-bw": 0},
-                {"rate-tc-index": 2, "rate-tc-bw": 0},
-                {"rate-tc-index": 3, "rate-tc-bw": 20},
-                {"rate-tc-index": 4, "rate-tc-bw": 80},
-                {"rate-tc-index": 5, "rate-tc-bw": 0},
-                {"rate-tc-index": 6, "rate-tc-bw": 0},
-                {"rate-tc-index": 7, "rate-tc-bw": 0},
+                {"index": 0, "bw": 0},
+                {"index": 1, "bw": 0},
+                {"index": 2, "bw": 0},
+                {"index": 3, "bw": 20},
+                {"index": 4, "bw": 80},
+                {"index": 5, "bw": 0},
+                {"index": 6, "bw": 0},
+                {"index": 7, "bw": 0},
             ]
         })
     except NlError as exc: