net: introduce ndo_set_rx_mode_async and netdev_rx_mode_work

Add ndo_set_rx_mode_async callback that drivers can implement instead
of the legacy ndo_set_rx_mode. The legacy callback runs under the
netif_addr_lock spinlock with BHs disabled, preventing drivers from
sleeping. The async variant runs from a work queue with rtnl_lock and
netdev_lock_ops held, in fully sleepable context.

When __dev_set_rx_mode() sees ndo_set_rx_mode_async, it schedules
netdev_rx_mode_work instead of calling the driver inline. The work
function takes two snapshots of each address list (uc/mc) under
the addr_lock, then drops the lock and calls the driver with the
work copies. After the driver returns, it reconciles the snapshots
back to the real lists under the lock.

Add netif_rx_mode_sync() to opportunistically execute the pending
workqueue update inline, so that rx mode changes are committed
before returning to userspace:
  - dev_change_flags (SIOCSIFFLAGS / RTM_NEWLINK)
  - dev_set_promiscuity
  - dev_set_allmulti
  - dev_ifsioc SIOCADDMULTI / SIOCDELMULTI
  - do_setlink (RTM_SETLINK)

Note that some deep hierarchies still do skip the lower updates via:
  - dev_uc_sync
  - dev_mc_sync

If we do end up hitting user-visible issues, we can add more calls to
netif_rx_mode_sync in specific places. But hopefully we should not,
the actual user-visible lists are still synced, it's that just HW state
that might be lagging.

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20260416185712.2155425-3-sdf@fomichev.me
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c
index 7a8966544c9d..f3979b276090 100644
--- a/net/core/dev_ioctl.c
+++ b/net/core/dev_ioctl.c
@@ -586,24 +586,26 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, void __user *data,
 		return err;
 
 	case SIOCADDMULTI:
-		if (!ops->ndo_set_rx_mode ||
+		if ((!ops->ndo_set_rx_mode && !ops->ndo_set_rx_mode_async) ||
 		    ifr->ifr_hwaddr.sa_family != AF_UNSPEC)
 			return -EINVAL;
 		if (!netif_device_present(dev))
 			return -ENODEV;
 		netdev_lock_ops(dev);
 		err = dev_mc_add_global(dev, ifr->ifr_hwaddr.sa_data);
+		netif_rx_mode_sync(dev);
 		netdev_unlock_ops(dev);
 		return err;
 
 	case SIOCDELMULTI:
-		if (!ops->ndo_set_rx_mode ||
+		if ((!ops->ndo_set_rx_mode && !ops->ndo_set_rx_mode_async) ||
 		    ifr->ifr_hwaddr.sa_family != AF_UNSPEC)
 			return -EINVAL;
 		if (!netif_device_present(dev))
 			return -ENODEV;
 		netdev_lock_ops(dev);
 		err = dev_mc_del_global(dev, ifr->ifr_hwaddr.sa_data);
+		netif_rx_mode_sync(dev);
 		netdev_unlock_ops(dev);
 		return err;