net: protect threaded status of NAPI with netdev_lock()

Now that NAPI instances can't come and go without holding
netdev->lock we can trivially switch from rtnl_lock() to
netdev_lock() for setting netdev->threaded via sysfs.

Note that since we do not lock netdev_lock around sysfs
calls in the core we don't have to "trylock" like we do
with rtnl_lock.

Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115035319.559603-9-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 3941e4d0073e1fd7d5603ecfd82ec1839593155e..20e773bbd1819fdf8720db418599c6225f2ceb55 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -384,7 +384,7 @@ struct napi_struct {
        int                     rx_count; /* length of rx_list */
        unsigned int            napi_id; /* protected by netdev_lock */
        struct hrtimer          timer;
-       struct task_struct      *thread;
+       struct task_struct      *thread; /* protected by netdev_lock */
        unsigned long           gro_flush_timeout;
        unsigned long           irq_suspend_timeout;
        u32                     defer_hard_irqs;
@@ -2451,11 +2451,13 @@ struct net_device {
         * Drivers are free to use it for other protection.
         *
         * Protects:
-        *      @napi_list, @net_shaper_hierarchy, @reg_state
+        *      @napi_list, @net_shaper_hierarchy, @reg_state, @threaded
         *
         * Partially protects (writers must hold both @lock and rtnl_lock):
         *      @up
         *
+        * Also protects some fields in struct napi_struct.
+        *
         * Ordering: take after rtnl_lock.
         */
        struct mutex            lock;
@@ -2697,6 +2699,13 @@ static inline void netdev_assert_locked(struct net_device *dev)
        lockdep_assert_held(&dev->lock);
 }
 
+static inline void netdev_assert_locked_or_invisible(struct net_device *dev)
+{
+       if (dev->reg_state == NETREG_REGISTERED ||
+           dev->reg_state == NETREG_UNREGISTERING)
+               netdev_assert_locked(dev);
+}
+
 static inline void netif_napi_set_irq(struct napi_struct *napi, int irq)
 {
        napi->irq = irq;

diff --git a/net/core/dev.c b/net/core/dev.c
index 2ef50a3ee4a18f2ce26079ac4ef12d836191bf84..34db90f345d54d5a9b89590400ac12f137149d35 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6785,6 +6785,8 @@ int dev_set_threaded(struct net_device *dev, bool threaded)
        struct napi_struct *napi;
        int err = 0;
 
+       netdev_assert_locked_or_invisible(dev);
+
        if (dev->threaded == threaded)
                return 0;
 

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 2d9afc6e2161efa51ffa62813ec10c8f43944bce..9365a7185a1d11f4e799bb88110cdb5ea2c008ab 100644 (file)
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -36,7 +36,7 @@ static const char fmt_uint[] = "%u\n";
 static const char fmt_ulong[] = "%lu\n";
 static const char fmt_u64[] = "%llu\n";
 
-/* Caller holds RTNL or RCU */
+/* Caller holds RTNL, netdev->lock or RCU */
 static inline int dev_isalive(const struct net_device *dev)
 {
        return READ_ONCE(dev->reg_state) <= NETREG_REGISTERED;
@@ -108,6 +108,36 @@ static ssize_t netdev_store(struct device *dev, struct device_attribute *attr,
        return ret;
 }
 
+/* Same as netdev_store() but takes netdev_lock() instead of rtnl_lock() */
+static ssize_t
+netdev_lock_store(struct device *dev, struct device_attribute *attr,
+                 const char *buf, size_t len,
+                 int (*set)(struct net_device *, unsigned long))
+{
+       struct net_device *netdev = to_net_dev(dev);
+       struct net *net = dev_net(netdev);
+       unsigned long new;
+       int ret;
+
+       if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
+               return -EPERM;
+
+       ret = kstrtoul(buf, 0, &new);
+       if (ret)
+               return ret;
+
+       netdev_lock(netdev);
+
+       if (dev_isalive(netdev)) {
+               ret = (*set)(netdev, new);
+               if (ret == 0)
+                       ret = len;
+       }
+       netdev_unlock(netdev);
+
+       return ret;
+}
+
 NETDEVICE_SHOW_RO(dev_id, fmt_hex);
 NETDEVICE_SHOW_RO(dev_port, fmt_dec);
 NETDEVICE_SHOW_RO(addr_assign_type, fmt_dec);
@@ -638,7 +668,7 @@ static ssize_t threaded_store(struct device *dev,
                              struct device_attribute *attr,
                              const char *buf, size_t len)
 {
-       return netdev_store(dev, attr, buf, len, modify_napi_threaded);
+       return netdev_lock_store(dev, attr, buf, len, modify_napi_threaded);
 }
 static DEVICE_ATTR_RW(threaded);