[PATCH v3 net-next 0/4] net: introduce rps_default_mask

[PATCH v3 net-next 0/4] net: introduce rps_default_mask

[Paolo Abeni]

Real-time setups try hard to ensure proper isolation between time
critical applications and e.g. network processing performed by the
network stack in softirq and RPS is used to move the softirq 
activity away from the isolated core.

If the network configuration is dynamic, with netns and devices
routinely created at run-time, enforcing the correct RPS setting
on each newly created device allowing to transient bad configuration
became complex.

Additionally, when multi-queue devices are involved, configuring rps
in user-space on each queue easily becomes very expensive, e.g.
some setups use veths with per cpu queues.

These series try to address the above, introducing a new
sysctl knob: rps_default_mask. The new sysctl entry allows
configuring a netns-wide RPS mask, to be enforced since receive 
queue creation time without any fourther per device configuration
required.

Additionally, a simple self-test is introduced to check the 
rps_default_mask behavior.

v2 -> v3:
 - reduce code duplication
 - rebased

Paolo Abeni (4):
  net-sysctl: factor out cpumask parsing helper
  net-sysctl: factor-out rpm mask manipulation helpers
  net: introduce default_rps_mask netns attribute
  self-tests: introduce self-tests for RPS default mask

 Documentation/admin-guide/sysctl/net.rst      |  6 ++
 include/linux/netdevice.h                     |  1 +
 net/core/dev.h                                |  2 +
 net/core/net-sysfs.c                          | 79 +++++++++++-------
 net/core/sysctl_net_core.c                    | 80 ++++++++++++++-----
 tools/testing/selftests/net/Makefile          |  1 +
 tools/testing/selftests/net/config            |  3 +
 .../testing/selftests/net/rps_default_mask.sh | 57 +++++++++++++
 8 files changed, 181 insertions(+), 48 deletions(-)
 create mode 100755 tools/testing/selftests/net/rps_default_mask.sh

-- 
2.39.1

[PATCH v3 net-next 1/4] net-sysctl: factor out cpumask parsing helper

[Paolo Abeni]

Will be used by the following patch to avoid code
duplication. No functional changes intended.

The only difference is that now flow_limit_cpu_sysctl() will
always compute the flow limit mask on each read operation,
even when read() will not return any byte to user-space.

Note that the new helper is placed under a new #ifdef at
the file start to better fit the usage in the later patch

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
new in v3
---
 net/core/sysctl_net_core.c | 45 +++++++++++++++++++++++---------------
 1 file changed, 27 insertions(+), 18 deletions(-)

diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index e7b98162c632..31a5adc1ba94 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -45,6 +45,32 @@ EXPORT_SYMBOL(sysctl_fb_tunnels_only_for_init_net);
 int sysctl_devconf_inherit_init_net __read_mostly;
 EXPORT_SYMBOL(sysctl_devconf_inherit_init_net);
 
+#if IS_ENABLED(CONFIG_NET_FLOW_LIMIT)
+void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos, struct cpumask *mask)
+{
+	char kbuf[128];
+	int len;
+
+	if (*ppos || !*lenp) {
+		*lenp = 0;
+		return;
+	}
+
+	len = min(sizeof(kbuf) - 1, *lenp);
+	len = scnprintf(kbuf, len, "%*pb", cpumask_pr_args(mask));
+	if (!len) {
+		*lenp = 0;
+		return;
+	}
+
+	if (len < *lenp)
+		kbuf[len++] = '\n';
+	memcpy(buffer, kbuf, len);
+	*lenp = len;
+	*ppos += len;
+}
+#endif
+
 #ifdef CONFIG_RPS
 static int rps_sock_flow_sysctl(struct ctl_table *table, int write,
 				void *buffer, size_t *lenp, loff_t *ppos)
@@ -155,13 +181,6 @@ static int flow_limit_cpu_sysctl(struct ctl_table *table, int write,
 write_unlock:
 		mutex_unlock(&flow_limit_update_mutex);
 	} else {
-		char kbuf[128];
-
-		if (*ppos || !*lenp) {
-			*lenp = 0;
-			goto done;
-		}
-
 		cpumask_clear(mask);
 		rcu_read_lock();
 		for_each_possible_cpu(i) {
@@ -171,17 +190,7 @@ static int flow_limit_cpu_sysctl(struct ctl_table *table, int write,
 		}
 		rcu_read_unlock();
 
-		len = min(sizeof(kbuf) - 1, *lenp);
-		len = scnprintf(kbuf, len, "%*pb", cpumask_pr_args(mask));
-		if (!len) {
-			*lenp = 0;
-			goto done;
-		}
-		if (len < *lenp)
-			kbuf[len++] = '\n';
-		memcpy(buffer, kbuf, len);
-		*lenp = len;
-		*ppos += len;
+		dump_cpumask(buffer, lenp, ppos, mask);
 	}
 
 done:
-- 
2.39.1

[PATCH v3 net-next 2/4] net-sysctl: factor-out rpm mask manipulation helpers

[Paolo Abeni]

Will simplify the following patch. No functional change
intended.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v2 -> v3: factor out the new rps_cpumask_housekeeping() helper
---
 net/core/dev.h       |  2 ++
 net/core/net-sysfs.c | 72 ++++++++++++++++++++++++++------------------
 2 files changed, 44 insertions(+), 30 deletions(-)

diff --git a/net/core/dev.h b/net/core/dev.h
index a065b7571441..e075e198092c 100644
--- a/net/core/dev.h
+++ b/net/core/dev.h
@@ -9,6 +9,7 @@ struct net_device;
 struct netdev_bpf;
 struct netdev_phys_item_id;
 struct netlink_ext_ack;
+struct cpumask;
 
 /* Random bits of netdevice that don't need to be exposed */
 #define FLOW_LIMIT_HISTORY	(1 << 7)  /* must be ^2 and !overflow buckets */
@@ -134,4 +135,5 @@ static inline void netif_set_gro_ipv4_max_size(struct net_device *dev,
 	WRITE_ONCE(dev->gro_ipv4_max_size, size);
 }
 
+int rps_cpumask_housekeeping(struct cpumask *mask);
 #endif
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index ca55dd747d6c..2126970a4bfd 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -831,42 +831,18 @@ static ssize_t show_rps_map(struct netdev_rx_queue *queue, char *buf)
 	return len < PAGE_SIZE ? len : -EINVAL;
 }
 
-static ssize_t store_rps_map(struct netdev_rx_queue *queue,
-			     const char *buf, size_t len)
+static int netdev_rx_queue_set_rps_mask(struct netdev_rx_queue *queue,
+					cpumask_var_t mask)
 {
-	struct rps_map *old_map, *map;
-	cpumask_var_t mask;
-	int err, cpu, i;
 	static DEFINE_MUTEX(rps_map_mutex);
-
-	if (!capable(CAP_NET_ADMIN))
-		return -EPERM;
-
-	if (!alloc_cpumask_var(&mask, GFP_KERNEL))
-		return -ENOMEM;
-
-	err = bitmap_parse(buf, len, cpumask_bits(mask), nr_cpumask_bits);
-	if (err) {
-		free_cpumask_var(mask);
-		return err;
-	}
-
-	if (!cpumask_empty(mask)) {
-		cpumask_and(mask, mask, housekeeping_cpumask(HK_TYPE_DOMAIN));
-		cpumask_and(mask, mask, housekeeping_cpumask(HK_TYPE_WQ));
-		if (cpumask_empty(mask)) {
-			free_cpumask_var(mask);
-			return -EINVAL;
-		}
-	}
+	struct rps_map *old_map, *map;
+	int cpu, i;
 
 	map = kzalloc(max_t(unsigned int,
 			    RPS_MAP_SIZE(cpumask_weight(mask)), L1_CACHE_BYTES),
 		      GFP_KERNEL);
-	if (!map) {
-		free_cpumask_var(mask);
+	if (!map)
 		return -ENOMEM;
-	}
 
 	i = 0;
 	for_each_cpu_and(cpu, mask, cpu_online_mask)
@@ -893,9 +869,45 @@ static ssize_t store_rps_map(struct netdev_rx_queue *queue,
 
 	if (old_map)
 		kfree_rcu(old_map, rcu);
+	return 0;
+}
 
+int rps_cpumask_housekeeping(struct cpumask *mask)
+{
+	if (!cpumask_empty(mask)) {
+		cpumask_and(mask, mask, housekeeping_cpumask(HK_TYPE_DOMAIN));
+		cpumask_and(mask, mask, housekeeping_cpumask(HK_TYPE_WQ));
+		if (cpumask_empty(mask))
+			return -EINVAL;
+	}
+	return 0;
+}
+
+static ssize_t store_rps_map(struct netdev_rx_queue *queue,
+			     const char *buf, size_t len)
+{
+	cpumask_var_t mask;
+	int err;
+
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	if (!alloc_cpumask_var(&mask, GFP_KERNEL))
+		return -ENOMEM;
+
+	err = bitmap_parse(buf, len, cpumask_bits(mask), nr_cpumask_bits);
+	if (err)
+		goto out;
+
+	err = rps_cpumask_housekeeping(mask);
+	if (err)
+		goto out;
+
+	err = netdev_rx_queue_set_rps_mask(queue, mask);
+
+out:
 	free_cpumask_var(mask);
-	return len;
+	return err ? : len;
 }
 
 static ssize_t show_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
-- 
2.39.1

[PATCH v3 net-next 3/4] net: introduce default_rps_mask netns attribute

[Paolo Abeni]

If RPS is enabled, this allows configuring a default rps
mask, which is effective since receive queue creation time.

A default RPS mask allows the system admin to ensure proper
isolation, avoiding races at network namespace or device
creation time.

The default RPS mask is initially empty, and can be
modified via a newly added sysctl entry.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v2 -> v3:
 - avoid a bit of code duplication thanks to new
   helpers in patch 1/4 and 2/4
---
 Documentation/admin-guide/sysctl/net.rst |  6 ++++
 include/linux/netdevice.h                |  1 +
 net/core/net-sysfs.c                     |  7 +++++
 net/core/sysctl_net_core.c               | 37 +++++++++++++++++++++++-
 4 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index 6394f5dc2303..466c560b0c30 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -215,6 +215,12 @@ rmem_max
 
 The maximum receive socket buffer size in bytes.
 
+rps_default_mask
+----------------
+
+The default RPS CPU mask used on newly created network devices. An empty
+mask means RPS disabled by default.
+
 tstamp_allow_data
 -----------------
 Allow processes to receive tx timestamps looped together with the original
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d5ef4c1fedd2..38ab96ae0d68 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -223,6 +223,7 @@ struct net_device_core_stats {
 #include <linux/static_key.h>
 extern struct static_key_false rps_needed;
 extern struct static_key_false rfs_needed;
+extern struct cpumask rps_default_mask;
 #endif
 
 struct neighbour;
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 2126970a4bfd..4b361ac6a252 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1083,6 +1083,13 @@ static int rx_queue_add_kobject(struct net_device *dev, int index)
 			goto err;
 	}
 
+#if IS_ENABLED(CONFIG_RPS) && IS_ENABLED(CONFIG_SYSCTL)
+	if (!cpumask_empty(&rps_default_mask)) {
+		error = netdev_rx_queue_set_rps_mask(queue, &rps_default_mask);
+		if (error)
+			goto err;
+	}
+#endif
 	kobject_uevent(kobj, KOBJ_ADD);
 
 	return error;
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 31a5adc1ba94..85666af57436 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -16,6 +16,7 @@
 #include <linux/vmalloc.h>
 #include <linux/init.h>
 #include <linux/slab.h>
+#include <linux/sched/isolation.h>
 
 #include <net/ip.h>
 #include <net/sock.h>
@@ -45,7 +46,7 @@ EXPORT_SYMBOL(sysctl_fb_tunnels_only_for_init_net);
 int sysctl_devconf_inherit_init_net __read_mostly;
 EXPORT_SYMBOL(sysctl_devconf_inherit_init_net);
 
-#if IS_ENABLED(CONFIG_NET_FLOW_LIMIT)
+#if IS_ENABLED(CONFIG_NET_FLOW_LIMIT) || IS_ENABLED(CONFIG_RPS)
 void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos, struct cpumask *mask)
 {
 	char kbuf[128];
@@ -72,6 +73,31 @@ void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos, struct cpumask *mask
 #endif
 
 #ifdef CONFIG_RPS
+struct cpumask rps_default_mask;
+
+static int rps_default_mask_sysctl(struct ctl_table *table, int write,
+				   void *buffer, size_t *lenp, loff_t *ppos)
+{
+	int err = 0;
+
+	rtnl_lock();
+	if (write) {
+		err = cpumask_parse(buffer, &rps_default_mask);
+		if (err)
+			goto done;
+
+		err = rps_cpumask_housekeeping(&rps_default_mask);
+		if (err)
+			goto done;
+	} else {
+		dump_cpumask(buffer, lenp, ppos, &rps_default_mask);
+	}
+
+done:
+	rtnl_unlock();
+	return err;
+}
+
 static int rps_sock_flow_sysctl(struct ctl_table *table, int write,
 				void *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -481,6 +507,11 @@ static struct ctl_table net_core_table[] = {
 		.mode		= 0644,
 		.proc_handler	= rps_sock_flow_sysctl
 	},
+	{
+		.procname	= "rps_default_mask",
+		.mode		= 0644,
+		.proc_handler	= rps_default_mask_sysctl
+	},
 #endif
 #ifdef CONFIG_NET_FLOW_LIMIT
 	{
@@ -684,6 +715,10 @@ static __net_initdata struct pernet_operations sysctl_core_ops = {
 
 static __init int sysctl_core_init(void)
 {
+#if IS_ENABLED(CONFIG_RPS)
+	cpumask_copy(&rps_default_mask, cpu_none_mask);
+#endif
+
 	register_net_sysctl(&init_net, "net/core", net_core_table);
 	return register_pernet_subsys(&sysctl_core_ops);
 }
-- 
2.39.1

[PATCH v3 net-next 4/4] self-tests: introduce self-tests for RPS default mask

[Paolo Abeni]

Ensure that RPS default mask changes take place on
all newly created netns/devices and don't affect
existing ones.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 tools/testing/selftests/net/Makefile          |  1 +
 tools/testing/selftests/net/config            |  3 +
 .../testing/selftests/net/rps_default_mask.sh | 57 +++++++++++++++++++
 3 files changed, 61 insertions(+)
 create mode 100755 tools/testing/selftests/net/rps_default_mask.sh

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 951bd5342bc6..3364c548a23b 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -46,6 +46,7 @@ TEST_PROGS += stress_reuseport_listen.sh
 TEST_PROGS += l2_tos_ttl_inherit.sh
 TEST_PROGS += bind_bhash.sh
 TEST_PROGS += ip_local_port_range.sh
+TEST_PROGS += rps_default_mask.sh
 TEST_PROGS_EXTENDED := in_netns.sh setup_loopback.sh setup_veth.sh
 TEST_PROGS_EXTENDED += toeplitz_client.sh toeplitz.sh
 TEST_GEN_FILES =  socket nettest
diff --git a/tools/testing/selftests/net/config b/tools/testing/selftests/net/config
index bd89198cd817..cc9fd55ab869 100644
--- a/tools/testing/selftests/net/config
+++ b/tools/testing/selftests/net/config
@@ -3,6 +3,9 @@ CONFIG_NET_NS=y
 CONFIG_BPF_SYSCALL=y
 CONFIG_TEST_BPF=m
 CONFIG_NUMA=y
+CONFIG_RPS=y
+CONFIG_SYSFS=y
+CONFIG_PROC_SYSCTL=y
 CONFIG_NET_VRF=y
 CONFIG_NET_L3_MASTER_DEV=y
 CONFIG_IPV6=y
diff --git a/tools/testing/selftests/net/rps_default_mask.sh b/tools/testing/selftests/net/rps_default_mask.sh
new file mode 100755
index 000000000000..c81c0ac7ddfe
--- /dev/null
+++ b/tools/testing/selftests/net/rps_default_mask.sh
@@ -0,0 +1,57 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+readonly ksft_skip=4
+readonly cpus=$(nproc)
+ret=0
+
+[ $cpus -gt 2 ] || exit $ksft_skip
+
+readonly INITIAL_RPS_DEFAULT_MASK=$(cat /proc/sys/net/core/rps_default_mask)
+readonly NETNS="ns-$(mktemp -u XXXXXX)"
+
+setup() {
+	ip netns add "${NETNS}"
+	ip -netns "${NETNS}" link set lo up
+}
+
+cleanup() {
+	echo $INITIAL_RPS_DEFAULT_MASK > /proc/sys/net/core/rps_default_mask
+	ip netns del $NETNS
+}
+
+chk_rps() {
+	local rps_mask expected_rps_mask=$3
+	local dev_name=$2
+	local msg=$1
+
+	rps_mask=$(ip netns exec $NETNS cat /sys/class/net/$dev_name/queues/rx-0/rps_cpus)
+	printf "%-60s" "$msg"
+	if [ $rps_mask -eq $expected_rps_mask ]; then
+		echo "[ ok ]"
+	else
+		echo "[fail] expected $expected_rps_mask found $rps_mask"
+		ret=1
+	fi
+}
+
+trap cleanup EXIT
+
+echo 0 > /proc/sys/net/core/rps_default_mask
+setup
+chk_rps "empty rps_default_mask" lo 0
+cleanup
+
+echo 1 > /proc/sys/net/core/rps_default_mask
+setup
+chk_rps "non zero rps_default_mask" lo 1
+
+echo 3 > /proc/sys/net/core/rps_default_mask
+chk_rps "changing rps_default_mask dont affect existing netns" lo 1
+
+ip -n $NETNS link add type veth
+ip -n $NETNS link set dev veth0 up
+ip -n $NETNS link set dev veth1 up
+chk_rps "changing rps_default_mask affect newly created devices" veth0 3
+chk_rps "changing rps_default_mask affect newly created devices[II]" veth1 3
+exit $ret
-- 
2.39.1

Re: [PATCH v3 net-next 1/4] net-sysctl: factor out cpumask parsing helper

[kernel test robot]

Hi Paolo,

I love your patch! Perhaps something to improve:

[auto build test WARNING on net-next/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Paolo-Abeni/net-sysctl-factor-out-cpumask-parsing-helper/20230207-023315
patch link:    https://lore.kernel.org/r/f171c4f78c17c259deb0cae78a26dc274afe9fce.1675708062.git.pabeni%40redhat.com
patch subject: [PATCH v3 net-next 1/4] net-sysctl: factor out cpumask parsing helper
config: ia64-allyesconfig (https://download.01.org/0day-ci/archive/20230207/202302070311.gE92izdH-lkp@intel.com/config)
compiler: ia64-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/f4b9914b6f1b7a7b3e416e1ef67db9ce6ad87f38
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Paolo-Abeni/net-sysctl-factor-out-cpumask-parsing-helper/20230207-023315
        git checkout f4b9914b6f1b7a7b3e416e1ef67db9ce6ad87f38
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=ia64 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=ia64 SHELL=/bin/bash net/core/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> net/core/sysctl_net_core.c:49:6: warning: no previous prototype for 'dump_cpumask' [-Wmissing-prototypes]
      49 | void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos, struct cpumask *mask)
         |      ^~~~~~~~~~~~


vim +/dump_cpumask +49 net/core/sysctl_net_core.c

    47	
    48	#if IS_ENABLED(CONFIG_NET_FLOW_LIMIT)
  > 49	void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos, struct cpumask *mask)
    50	{
    51		char kbuf[128];
    52		int len;
    53	
    54		if (*ppos || !*lenp) {
    55			*lenp = 0;
    56			return;
    57		}
    58	
    59		len = min(sizeof(kbuf) - 1, *lenp);
    60		len = scnprintf(kbuf, len, "%*pb", cpumask_pr_args(mask));
    61		if (!len) {
    62			*lenp = 0;
    63			return;
    64		}
    65	
    66		if (len < *lenp)
    67			kbuf[len++] = '\n';
    68		memcpy(buffer, kbuf, len);
    69		*lenp = len;
    70		*ppos += len;
    71	}
    72	#endif
    73	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests

Re: [PATCH v3 net-next 1/4] net-sysctl: factor out cpumask parsing helper

[kernel test robot]

Hi Paolo,

I love your patch! Perhaps something to improve:

[auto build test WARNING on net-next/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Paolo-Abeni/net-sysctl-factor-out-cpumask-parsing-helper/20230207-023315
patch link:    https://lore.kernel.org/r/f171c4f78c17c259deb0cae78a26dc274afe9fce.1675708062.git.pabeni%40redhat.com
patch subject: [PATCH v3 net-next 1/4] net-sysctl: factor out cpumask parsing helper
config: i386-randconfig-a004-20230206 (https://download.01.org/0day-ci/archive/20230207/202302071859.cwSYKxyV-lkp@intel.com/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/f4b9914b6f1b7a7b3e416e1ef67db9ce6ad87f38
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Paolo-Abeni/net-sysctl-factor-out-cpumask-parsing-helper/20230207-023315
        git checkout f4b9914b6f1b7a7b3e416e1ef67db9ce6ad87f38
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash net/core/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> net/core/sysctl_net_core.c:49:6: warning: no previous prototype for function 'dump_cpumask' [-Wmissing-prototypes]
   void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos, struct cpumask *mask)
        ^
   net/core/sysctl_net_core.c:49:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos, struct cpumask *mask)
   ^
   static 
   1 warning generated.


vim +/dump_cpumask +49 net/core/sysctl_net_core.c

    47	
    48	#if IS_ENABLED(CONFIG_NET_FLOW_LIMIT)
  > 49	void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos, struct cpumask *mask)
    50	{
    51		char kbuf[128];
    52		int len;
    53	
    54		if (*ppos || !*lenp) {
    55			*lenp = 0;
    56			return;
    57		}
    58	
    59		len = min(sizeof(kbuf) - 1, *lenp);
    60		len = scnprintf(kbuf, len, "%*pb", cpumask_pr_args(mask));
    61		if (!len) {
    62			*lenp = 0;
    63			return;
    64		}
    65	
    66		if (len < *lenp)
    67			kbuf[len++] = '\n';
    68		memcpy(buffer, kbuf, len);
    69		*lenp = len;
    70		*ppos += len;
    71	}
    72	#endif
    73	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests