Re: [PATCH net-next v5 03/14] net: move promiscuity handling into netdev_rx_mode_work

[Jakub Kicinski <kuba@kernel.org>]

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---
net: move promiscuity handling into netdev_rx_mode_work

This commit moves unicast promiscuity tracking into netdev_rx_mode_work so
it runs under netdev_ops_lock instead of the addr_lock spinlock. It also
changes ASSERT_RTNL() to netdev_ops_assert_locked() in several functions
called from the work queue.

> diff --git a/net/core/dev.c b/net/core/dev.c
> index 0efac0c730077..08dac9c759996 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -9586,7 +9586,7 @@ int __dev_set_promiscuity(struct net_device *dev, int inc, bool notify)
>  	kuid_t uid;
>  	kgid_t gid;
>  
> -	ASSERT_RTNL();
> +	netdev_ops_assert_locked(dev);

Can this cause a lockdep assertion failure for unconverted ops-locked devices
using the legacy RX mode path?

Replacing ASSERT_RTNL() with netdev_ops_assert_locked(dev) asserts that
dev->lock is held for devices where netdev_need_ops_lock(dev) is true.

[ ... ]

> diff --git a/net/core/dev_addr_lists.c b/net/core/dev_addr_lists.c
> index a05db3ac43ea9..61589537b2d3d 100644
> --- a/net/core/dev_addr_lists.c
> +++ b/net/core/dev_addr_lists.c
[ ... ]
> @@ -1295,20 +1337,16 @@ void __dev_set_rx_mode(struct net_device *dev)
>  	if (!netif_device_present(dev))
>  		return;
>  
> -	if (ops->ndo_set_rx_mode_async) {
> +	if (ops->ndo_set_rx_mode_async || ops->ndo_change_rx_flags) {
>  		netif_rx_mode_queue(dev);
>  		return;
>  	}
>  
> -	if (!(dev->priv_flags & IFF_UNICAST_FLT)) {
> -		if (!netdev_uc_empty(dev) && !dev->uc_promisc) {
> -			__dev_set_promiscuity(dev, 1, false);
> -			dev->uc_promisc = true;
> -		} else if (netdev_uc_empty(dev) && dev->uc_promisc) {
> -			__dev_set_promiscuity(dev, -1, false);
> -			dev->uc_promisc = false;
> -		}
> -	}
> +	/* Legacy path for non-ops-locked HW devices. */
> +
> +	promisc_inc = netif_uc_promisc_update(dev);
> +	if (promisc_inc)
> +		__dev_set_promiscuity(dev, promisc_inc, false);

If an ops-locked device has not yet been converted to implement the new
ndo_set_rx_mode_async or ndo_change_rx_flags callbacks, this legacy path
will be executed.

When a secondary unicast address is added to such a device (e.g., by
bringing up a macvlan interface over it) and the device lacks
IFF_UNICAST_FLT, netif_uc_promisc_update() returns 1. This triggers a
synchronous inline call to __dev_set_promiscuity(dev, 1, false).

Since __dev_set_rx_mode() is invoked from address list helpers like
dev_uc_add() which only hold rtnl_lock() and netif_addr_lock_bh(dev),
dev->lock is not held, which would trigger the new assertion in
__dev_set_promiscuity().