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>

Author: kuba-moo

drivers/net/phy/phy_device.c

@@ -1935,6 +1935,9 @@ void phy_detach(struct phy_device *phydev)
 	if (dev) {
 		struct hwtstamp_provider *hwprov;
 
+		/* hwprov may technically be protected by ops lock but
+		 * not for devices with a phydev, see phy_link_topo_add_phy()
+		 */
 		hwprov = rtnl_dereference(dev->hwprov);
 		/* Disable timestamp if it is the one selected */
 		if (hwprov && hwprov->phydev == phydev) {

drivers/net/phy/phy_link_topology.c

@@ -38,7 +38,9 @@ int phy_link_topo_add_phy(struct net_device *dev,
 
 	/* ethtool ops may run without rtnl_lock, and rtnl_lock is what
 	 * currently protects the PHY topology. No driver currently mixes
-	 * the two, flag if someone tries. See also ethnl_req_get_phydev().
+	 * the two, flag if someone tries. See also:
+	 *  - ethnl_req_get_phydev()
+	 *  - phy_detach()
 	 */
 	if (WARN_ON_ONCE(netdev_need_ops_lock(dev)))
 		return -EOPNOTSUPP;

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
 	 *

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);
 

net/core/dev_ioctl.c

@@ -260,7 +260,7 @@ int dev_get_hwtstamp_phylib(struct net_device *dev,
 {
 	struct hwtstamp_provider *hwprov;
 
-	hwprov = rtnl_dereference(dev->hwprov);
+	hwprov = netdev_ops_lock_dereference(dev->hwprov, dev);
 	if (hwprov) {
 		cfg->qualifier = hwprov->desc.qualifier;
 		if (hwprov->source == HWTSTAMP_SOURCE_PHYLIB &&
@@ -337,7 +337,7 @@ int dev_set_hwtstamp_phylib(struct net_device *dev,
 	bool phy_ts;
 	int err;
 
-	hwprov = rtnl_dereference(dev->hwprov);
+	hwprov = netdev_ops_lock_dereference(dev->hwprov, dev);
 	if (hwprov) {
 		if (hwprov->source == HWTSTAMP_SOURCE_PHYLIB &&
 		    hwprov->phydev) {

net/ethtool/tsconfig.c

@@ -2,6 +2,7 @@
 
 #include <linux/net_tstamp.h>
 #include <linux/ptp_clock_kernel.h>
+#include <net/netdev_lock.h>
 
 #include "bitset.h"
 #include "common.h"
@@ -57,7 +58,7 @@ static int tsconfig_prepare_data(const struct ethnl_req_info *req_base,
 	data->hwtst_config.flags = cfg.flags;
 
 	data->hwprov_desc.index = -1;
-	hwprov = rtnl_dereference(dev->hwprov);
+	hwprov = netdev_ops_lock_dereference(dev->hwprov, dev);
 	if (hwprov) {
 		data->hwprov_desc.index = hwprov->desc.index;
 		data->hwprov_desc.qualifier = hwprov->desc.qualifier;
@@ -213,7 +214,7 @@ static int tsconfig_send_reply(struct net_device *dev, struct genl_info *info)
 		return -ENOMEM;
 	}
 
-	ASSERT_RTNL();
+	netdev_assert_locked_ops_compat(dev);
 	reply_data->base.dev = dev;
 	ret = tsconfig_prepare_data(&req_info->base, &reply_data->base, info);
 	if (ret < 0)
@@ -316,7 +317,7 @@ static int ethnl_set_tsconfig(struct ethnl_req_info *req_base,
 		struct hwtstamp_provider_desc __hwprov_desc = {.index = -1};
 		struct hwtstamp_provider *__hwprov;
 
-		__hwprov = rtnl_dereference(dev->hwprov);
+		__hwprov = netdev_ops_lock_dereference(dev->hwprov, dev);
 		if (__hwprov) {
 			__hwprov_desc.index = __hwprov->desc.index;
 			__hwprov_desc.qualifier = __hwprov->desc.qualifier;
@@ -414,7 +415,8 @@ static int ethnl_set_tsconfig(struct ethnl_req_info *req_base,
 			goto err_free_hwprov;
 
 		/* Change the selected hwtstamp source */
-		__hwprov = rcu_replace_pointer_rtnl(dev->hwprov, hwprov);
+		__hwprov = rcu_replace_pointer(dev->hwprov, hwprov,
+					       netdev_is_locked_ops_compat(dev));
 		if (__hwprov)
 			kfree_rcu(__hwprov, rcu_head);
 	}