[PATCH net-next v2 06/11] net: designate queue -> napi linking as "ops protected"

[Jakub Kicinski <kuba@kernel.org>]

netdev netlink is the only reader of netdev_{,rx_}queue->napi,
and it already holds netdev->lock. Switch protection of
the writes to netdev->lock to "ops protected".

The expectation will be now that accessing queue->napi
will require netdev->lock for "ops locked" drivers, and
rtnl_lock for all other drivers.

Current "ops locked" drivers don't require any changes.
gve and netdevsim use _locked() helpers right next to
netif_queue_set_napi() so they must be holding the instance
lock. iavf doesn't call it. bnxt is a bit messy but all paths
seem locked.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 include/linux/netdevice.h     | 5 +++--
 include/net/netdev_lock.h     | 8 ++++++++
 include/net/netdev_rx_queue.h | 2 +-
 net/core/dev.c                | 3 +--
 4 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 3dbce9cd3f5a..fd508e9f148c 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -710,7 +710,7 @@ struct netdev_queue {
  * slow- / control-path part
  */
 	/* NAPI instance for the queue
-	 * Readers and writers must hold RTNL
+	 * "ops protected", see comment about net_device::lock
 	 */
 	struct napi_struct	*napi;
 
@@ -2522,7 +2522,8 @@ struct net_device {
 	 * Double ops protects:
 	 *	@real_num_rx_queues, @real_num_tx_queues
 	 *
-	 * Also protects some fields in struct napi_struct.
+	 * Also protects some fields in:
+	 *	struct napi_struct, struct netdev_queue, struct netdev_rx_queue
 	 *
 	 * Ordering: take after rtnl_lock.
 	 */
diff --git a/include/net/netdev_lock.h b/include/net/netdev_lock.h
index efd302375ef2..1c0c9a94cc22 100644
--- a/include/net/netdev_lock.h
+++ b/include/net/netdev_lock.h
@@ -56,6 +56,14 @@ static inline void netdev_ops_assert_locked(const struct net_device *dev)
 		ASSERT_RTNL();
 }
 
+static inline void
+netdev_ops_assert_locked_or_invisible(const struct net_device *dev)
+{
+	if (dev->reg_state == NETREG_REGISTERED ||
+	    dev->reg_state == NETREG_UNREGISTERING)
+		netdev_ops_assert_locked(dev);
+}
+
 static inline int netdev_lock_cmp_fn(const struct lockdep_map *a,
 				     const struct lockdep_map *b)
 {
diff --git a/include/net/netdev_rx_queue.h b/include/net/netdev_rx_queue.h
index af40842f229d..b2238b551dce 100644
--- a/include/net/netdev_rx_queue.h
+++ b/include/net/netdev_rx_queue.h
@@ -24,7 +24,7 @@ struct netdev_rx_queue {
 	struct xsk_buff_pool            *pool;
 #endif
 	/* NAPI instance for the queue
-	 * Readers and writers must hold RTNL
+	 * "ops protected", see comment about net_device::lock
 	 */
 	struct napi_struct		*napi;
 	struct pp_memory_provider_params mp_params;
diff --git a/net/core/dev.c b/net/core/dev.c
index aa99c91fd68f..690d46497b2f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6896,8 +6896,7 @@ void netif_queue_set_napi(struct net_device *dev, unsigned int queue_index,
 
 	if (WARN_ON_ONCE(napi && !napi->dev))
 		return;
-	if (dev->reg_state >= NETREG_REGISTERED)
-		ASSERT_RTNL();
+	netdev_ops_assert_locked_or_invisible(dev);
 
 	switch (type) {
 	case NETDEV_QUEUE_TYPE_RX:
-- 
2.49.0