Add support to set per-NAPI defer_hard_irqs and gro_flush_timeout.

Signed-off-by: Joe Damato <jdamato@fastly.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
---
 Documentation/netlink/specs/netdev.yaml | 11 ++++++
 include/uapi/linux/netdev.h             |  1 +
 net/core/netdev-genl-gen.c              | 18 ++++++++++
 net/core/netdev-genl-gen.h              |  1 +
 net/core/netdev-genl.c                  | 45 +++++++++++++++++++++++++
 tools/include/uapi/linux/netdev.h       |  1 +
 6 files changed, 77 insertions(+)

diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
index 7b47454c51dd..f9cb97d6106c 100644
--- a/Documentation/netlink/specs/netdev.yaml
+++ b/Documentation/netlink/specs/netdev.yaml
@@ -693,6 +693,17 @@ operations:
         reply:
           attributes:
             - id
+    -
+      name: napi-set
+      doc: Set configurable NAPI instance settings.
+      attribute-set: napi
+      flags: [ admin-perm ]
+      do:
+        request:
+          attributes:
+            - id
+            - defer-hard-irqs
+            - gro-flush-timeout
 
 kernel-family:
   headers: [ "linux/list.h"]
diff --git a/include/uapi/linux/netdev.h b/include/uapi/linux/netdev.h
index cacd33359c76..e3ebb49f60d2 100644
--- a/include/uapi/linux/netdev.h
+++ b/include/uapi/linux/netdev.h
@@ -201,6 +201,7 @@ enum {
 	NETDEV_CMD_NAPI_GET,
 	NETDEV_CMD_QSTATS_GET,
 	NETDEV_CMD_BIND_RX,
+	NETDEV_CMD_NAPI_SET,
 
 	__NETDEV_CMD_MAX,
 	NETDEV_CMD_MAX = (__NETDEV_CMD_MAX - 1)
diff --git a/net/core/netdev-genl-gen.c b/net/core/netdev-genl-gen.c
index b28424ae06d5..e197bd84997c 100644
--- a/net/core/netdev-genl-gen.c
+++ b/net/core/netdev-genl-gen.c
@@ -22,6 +22,10 @@ static const struct netlink_range_validation netdev_a_page_pool_ifindex_range =
 	.max	= 2147483647ULL,
 };
 
+static const struct netlink_range_validation netdev_a_napi_defer_hard_irqs_range = {
+	.max	= 2147483647ULL,
+};
+
 /* Common nested types */
 const struct nla_policy netdev_page_pool_info_nl_policy[NETDEV_A_PAGE_POOL_IFINDEX + 1] = {
 	[NETDEV_A_PAGE_POOL_ID] = NLA_POLICY_FULL_RANGE(NLA_UINT, &netdev_a_page_pool_id_range),
@@ -87,6 +91,13 @@ static const struct nla_policy netdev_bind_rx_nl_policy[NETDEV_A_DMABUF_FD + 1]
 	[NETDEV_A_DMABUF_QUEUES] = NLA_POLICY_NESTED(netdev_queue_id_nl_policy),
 };
 
+/* NETDEV_CMD_NAPI_SET - do */
+static const struct nla_policy netdev_napi_set_nl_policy[NETDEV_A_NAPI_GRO_FLUSH_TIMEOUT + 1] = {
+	[NETDEV_A_NAPI_ID] = { .type = NLA_U32, },
+	[NETDEV_A_NAPI_DEFER_HARD_IRQS] = NLA_POLICY_FULL_RANGE(NLA_U32, &netdev_a_napi_defer_hard_irqs_range),
+	[NETDEV_A_NAPI_GRO_FLUSH_TIMEOUT] = { .type = NLA_UINT, },
+};
+
 /* Ops table for netdev */
 static const struct genl_split_ops netdev_nl_ops[] = {
 	{
@@ -171,6 +182,13 @@ static const struct genl_split_ops netdev_nl_ops[] = {
 		.maxattr	= NETDEV_A_DMABUF_FD,
 		.flags		= GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
 	},
+	{
+		.cmd		= NETDEV_CMD_NAPI_SET,
+		.doit		= netdev_nl_napi_set_doit,
+		.policy		= netdev_napi_set_nl_policy,
+		.maxattr	= NETDEV_A_NAPI_GRO_FLUSH_TIMEOUT,
+		.flags		= GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
+	},
 };
 
 static const struct genl_multicast_group netdev_nl_mcgrps[] = {
diff --git a/net/core/netdev-genl-gen.h b/net/core/netdev-genl-gen.h
index 8cda334fd042..e09dd7539ff2 100644
--- a/net/core/netdev-genl-gen.h
+++ b/net/core/netdev-genl-gen.h
@@ -33,6 +33,7 @@ int netdev_nl_napi_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb);
 int netdev_nl_qstats_get_dumpit(struct sk_buff *skb,
 				struct netlink_callback *cb);
 int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info);
+int netdev_nl_napi_set_doit(struct sk_buff *skb, struct genl_info *info);
 
 enum {
 	NETDEV_NLGRP_MGMT,
diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index ac19f2e6cfbe..b49c3b4e5fbe 100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -303,6 +303,51 @@ int netdev_nl_napi_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 	return err;
 }
 
+static int
+netdev_nl_napi_set_config(struct napi_struct *napi, struct genl_info *info)
+{
+	u64 gro_flush_timeout = 0;
+	u32 defer = 0;
+
+	if (info->attrs[NETDEV_A_NAPI_DEFER_HARD_IRQS]) {
+		defer = nla_get_u32(info->attrs[NETDEV_A_NAPI_DEFER_HARD_IRQS]);
+		napi_set_defer_hard_irqs(napi, defer);
+	}
+
+	if (info->attrs[NETDEV_A_NAPI_GRO_FLUSH_TIMEOUT]) {
+		gro_flush_timeout = nla_get_uint(info->attrs[NETDEV_A_NAPI_GRO_FLUSH_TIMEOUT]);
+		napi_set_gro_flush_timeout(napi, gro_flush_timeout);
+	}
+
+	return 0;
+}
+
+int netdev_nl_napi_set_doit(struct sk_buff *skb, struct genl_info *info)
+{
+	struct napi_struct *napi;
+	unsigned int napi_id;
+	int err;
+
+	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_NAPI_ID))
+		return -EINVAL;
+
+	napi_id = nla_get_u32(info->attrs[NETDEV_A_NAPI_ID]);
+
+	rtnl_lock();
+
+	napi = napi_by_id(napi_id);
+	if (napi) {
+		err = netdev_nl_napi_set_config(napi, info);
+	} else {
+		NL_SET_BAD_ATTR(info->extack, info->attrs[NETDEV_A_NAPI_ID]);
+		err = -ENOENT;
+	}
+
+	rtnl_unlock();
+
+	return err;
+}
+
 static int
 netdev_nl_queue_fill_one(struct sk_buff *rsp, struct net_device *netdev,
 			 u32 q_idx, u32 q_type, const struct genl_info *info)
diff --git a/tools/include/uapi/linux/netdev.h b/tools/include/uapi/linux/netdev.h
index cacd33359c76..e3ebb49f60d2 100644
--- a/tools/include/uapi/linux/netdev.h
+++ b/tools/include/uapi/linux/netdev.h
@@ -201,6 +201,7 @@ enum {
 	NETDEV_CMD_NAPI_GET,
 	NETDEV_CMD_QSTATS_GET,
 	NETDEV_CMD_BIND_RX,
+	NETDEV_CMD_NAPI_SET,
 
 	__NETDEV_CMD_MAX,
 	NETDEV_CMD_MAX = (__NETDEV_CMD_MAX - 1)
-- 
2.25.1

On 10/11/24 20:45, Joe Damato wrote:
> +int netdev_nl_napi_set_doit(struct sk_buff *skb, struct genl_info *info)
> +{
> +	struct napi_struct *napi;
> +	unsigned int napi_id;
> +	int err;
> +
> +	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_NAPI_ID))
> +		return -EINVAL;
> +
> +	napi_id = nla_get_u32(info->attrs[NETDEV_A_NAPI_ID]);
> +
> +	rtnl_lock();
> +
> +	napi = napi_by_id(napi_id);

AFAICS the above causes a RCU splat in the selftests:

https://netdev-3.bots.linux.dev/vmksft-net-dbg/results/856342/61-busy-poll-test-sh/stderr

because napi_by_id() only checks for the RCU lock.

Could you please have a look?

Thanks!

Paolo

On Tue, Nov 12, 2024 at 10:17:40AM +0100, Paolo Abeni wrote:
> On 10/11/24 20:45, Joe Damato wrote:
> > +int netdev_nl_napi_set_doit(struct sk_buff *skb, struct genl_info *info)
> > +{
> > +	struct napi_struct *napi;
> > +	unsigned int napi_id;
> > +	int err;
> > +
> > +	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_NAPI_ID))
> > +		return -EINVAL;
> > +
> > +	napi_id = nla_get_u32(info->attrs[NETDEV_A_NAPI_ID]);
> > +
> > +	rtnl_lock();
> > +
> > +	napi = napi_by_id(napi_id);
> 
> AFAICS the above causes a RCU splat in the selftests:
> 
> https://netdev-3.bots.linux.dev/vmksft-net-dbg/results/856342/61-busy-poll-test-sh/stderr
> 
> because napi_by_id() only checks for the RCU lock.
> 
> Could you please have a look?

Thanks for letting me know.

I rebuilt my kernel with CONFIG_PROVE_RCU_LIST and a couple other
debugging options and I was able to reproduce the splat you
mentioned.

I took a look and it looks like there might be two things:
  - netdev_nl_napi_set_doit needs to call rcu_read_lock /
    rcu_read_unlock, which would be a Fixes on the commit in the
    series just merged, and
  - netdev_nl_napi_get_doit also has the same issue and should be
    fixed in a separate commit with its own fixes tag.

If that sounds right to you, I'll propose a short series of 2
patches, 1 to fix each.

Let me know if that sounds OK?

In the meantime, I'm rebuilding a kernel now to ensure my proposed
fix fixes the splat.

On Fri, Oct 11, 2024 at 8:46 PM Joe Damato <jdamato@fastly.com> wrote:
>
> Add support to set per-NAPI defer_hard_irqs and gro_flush_timeout.
>
> Signed-off-by: Joe Damato <jdamato@fastly.com>
> Reviewed-by: Jakub Kicinski <kuba@kernel.org>

Reviewed-by: Eric Dumazet <edumazet@google.com>