net: ethtool: make dev->hwprov ops-protected

dev->hwprov tracks the active hwtstamp provider for the device.
Make it ops protected (instance lock if the netdev driver opts
into holding instance lock around callbacks, otherwise rtnl_lock).

hwprov is written and read in:
 - drivers/net/phy/phy_device.c
    phydev and ops protection don't currently mix, add a comment
 - net/ethtool/
    as of now holds both rtnl lock and ops lock, this one will
    soon only hold one lock or the other

read in:
 - net/core/dev_ioctl.c
    holds both rtnl lock and ops lock
 - net/core/timestamping.c
    RCU reader

The new netdev_ops_lock_dereference() helper does not have
"compat" in the name. The name would be quite long and I think
in this case it should be obvious that we need _a_ lock.
netdev_lock_dereference() already exists and means dev->lock
is always expected.

Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20260605002912.3456868-4-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 14 insertions, 0 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 74507c006490..a8709d0cc8d4 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2583,6 +2583,9 @@ struct net_device {
 	 * Double protects:
 	 *	@up, @moving_ns, @nd_net, @xdp_features
 	 *
+	 * Ops protects:
+	 *	@hwprov
+	 *
 	 * Double ops protects:
 	 *	@real_num_rx_queues, @real_num_tx_queues
 	 *
diff --git a/include/net/netdev_lock.h b/include/net/netdev_lock.h
index d3daec4e93f3..9fb3e93857c3 100644
--- a/include/net/netdev_lock.h
+++ b/include/net/netdev_lock.h
@@ -102,6 +102,14 @@ static inline void netdev_unlock_ops_compat(struct net_device *dev)
 		rtnl_unlock();
 }
 
+/* Matching "ops protected" category from netdevice.h */
+static inline int netdev_is_locked_ops_compat(const struct net_device *dev)
+{
+	if (netdev_need_ops_lock(dev))
+		return lockdep_is_held(&dev->lock);
+	return lockdep_rtnl_is_held();
+}
+
 static inline int netdev_lock_cmp_fn(const struct lockdep_map *a,
 				     const struct lockdep_map *b)
 {
@@ -138,6 +146,9 @@ static inline int netdev_lock_cmp_fn(const struct lockdep_map *a,
 #define netdev_lock_dereference(p, dev)				\
 	rcu_dereference_protected(p, lockdep_is_held(&(dev)->lock))
 
+#define netdev_ops_lock_dereference(p, dev)				\
+	rcu_dereference_protected(p, netdev_is_locked_ops_compat(dev))
+
 int netdev_debug_event(struct notifier_block *nb, unsigned long event,
 		       void *ptr);