net: remove RTNL use for /proc/sys/net/core/rps_default_mask

Use a dedicated mutex instead.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250702061558.1585870-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 28 insertions, 26 deletions

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index c9b969386399..8f897e2c8b4f 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1210,12 +1210,21 @@ static int rx_queue_default_mask(struct net_device *dev,
 				 struct netdev_rx_queue *queue)
 {
 #if IS_ENABLED(CONFIG_RPS) && IS_ENABLED(CONFIG_SYSCTL)
-	struct cpumask *rps_default_mask = READ_ONCE(dev_net(dev)->core.rps_default_mask);
+	struct cpumask *rps_default_mask;
+	int res = 0;
 
+	mutex_lock(&rps_default_mask_mutex);
+
+	rps_default_mask = dev_net(dev)->core.rps_default_mask;
 	if (rps_default_mask && !cpumask_empty(rps_default_mask))
-		return netdev_rx_queue_set_rps_mask(queue, rps_default_mask);
-#endif
+		res = netdev_rx_queue_set_rps_mask(queue, rps_default_mask);
+
+	mutex_unlock(&rps_default_mask_mutex);
+
+	return res;
+#else
 	return 0;
+#endif
 }
 
 static int rx_queue_add_kobject(struct net_device *dev, int index)
diff --git a/net/core/net-sysfs.h b/net/core/net-sysfs.h
index 8a5b04c2699a..e938f25e8e86 100644
--- a/net/core/net-sysfs.h
+++ b/net/core/net-sysfs.h
@@ -11,4 +11,6 @@ int netdev_queue_update_kobjects(struct net_device *net,
 int netdev_change_owner(struct net_device *, const struct net *net_old,
 			const struct net *net_new);
 
+extern struct mutex rps_default_mask_mutex;
+
 #endif
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 5dbb2c6f371d..8cf04b57ade1 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -28,6 +28,7 @@
 #include <net/rps.h>
 
 #include "dev.h"
+#include "net-sysfs.h"
 
 static int int_3600 = 3600;
 static int min_sndbuf = SOCK_MIN_SNDBUF;
@@ -96,50 +97,40 @@ free_buf:
 
 #ifdef CONFIG_RPS
 
-static struct cpumask *rps_default_mask_cow_alloc(struct net *net)
-{
-	struct cpumask *rps_default_mask;
-
-	if (net->core.rps_default_mask)
-		return net->core.rps_default_mask;
-
-	rps_default_mask = kzalloc(cpumask_size(), GFP_KERNEL);
-	if (!rps_default_mask)
-		return NULL;
-
-	/* pairs with READ_ONCE in rx_queue_default_mask() */
-	WRITE_ONCE(net->core.rps_default_mask, rps_default_mask);
-	return rps_default_mask;
-}
+DEFINE_MUTEX(rps_default_mask_mutex);
 
 static int rps_default_mask_sysctl(const struct ctl_table *table, int write,
 				   void *buffer, size_t *lenp, loff_t *ppos)
 {
 	struct net *net = (struct net *)table->data;
+	struct cpumask *mask;
 	int err = 0;
 
-	rtnl_lock();
+	mutex_lock(&rps_default_mask_mutex);
+	mask = net->core.rps_default_mask;
 	if (write) {
-		struct cpumask *rps_default_mask = rps_default_mask_cow_alloc(net);
-
+		if (!mask) {
+			mask = kzalloc(cpumask_size(), GFP_KERNEL);
+			net->core.rps_default_mask = mask;
+		}
 		err = -ENOMEM;
-		if (!rps_default_mask)
+		if (!mask)
 			goto done;
 
-		err = cpumask_parse(buffer, rps_default_mask);
+		err = cpumask_parse(buffer, mask);
 		if (err)
 			goto done;
 
-		err = rps_cpumask_housekeeping(rps_default_mask);
+		err = rps_cpumask_housekeeping(mask);
 		if (err)
 			goto done;
 	} else {
 		err = dump_cpumask(buffer, lenp, ppos,
-				   net->core.rps_default_mask ? : cpu_none_mask);
+				   mask ?: cpu_none_mask);
 	}
 
 done:
-	rtnl_unlock();
+	mutex_unlock(&rps_default_mask_mutex);
 	return err;
 }