Re: [PATCH net-next] net: ipv4: clear dev->ip_ptr before destroying inetdev

[Yuyang Huang]

On Fri, Jul 10, 2026 at 2:17 AM Ido Schimmel <idosch@xxxxxxxxxx> wrote:
>
> On Tue, Jul 07, 2026 at 01:30:39PM +0900, Yuyang Huang wrote:
> > To prevent RCU readers from accessing a partially destroyed in_device,
> > clear dev->ip_ptr early in inetdev_destroy() before freeing the
> > multicast list and individual IP addresses. This aligns the IPv4 teardown
> > sequence with the IPv6 implementation.
> >
> > Cc: Ido Schimmel <idosch@xxxxxxxxxx>
> > Cc: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> > Signed-off-by: Yuyang Huang <yuyanghuang@xxxxxxxxxx>
>
> I believe that sashiko-gemini [1] is right and you need to teach
> prestera to ignore NETDEV_DOWN notifications in the inetaddr chain when
> a RIF doesn't exist. Something like [2].
>
> Regarding ieee80211_ifa_changed(), the net device is being tore down, so
> failing to update the firmware ARP filter probably doesn't matter, but
> you can do something like [3] to avoid it completely.
>
> So, three patches where the last one aligns IPv4 with IPv6. Please check
> if other listeners need to be adjusted (mlxsw is OK).
>
> Thanks
>
> [1] https://sashiko.dev/#/patchset/20260707043039.101983-1-yuyanghuang%40google.com
>
> [2]
> diff --git a/drivers/net/ethernet/marvell/prestera/prestera_router.c b/drivers/net/ethernet/marvell/prestera/prestera_router.c
> index b036b173a308..0c4f462baa6e 100644
> --- a/drivers/net/ethernet/marvell/prestera/prestera_router.c
> +++ b/drivers/net/ethernet/marvell/prestera/prestera_router.c
> @@ -1302,10 +1302,8 @@ static int __prestera_inetaddr_port_event(struct net_device *port_dev,
>                 dev_hold(port_dev);
>                 break;
>         case NETDEV_DOWN:
> -               if (!re) {
> -                       NL_SET_ERR_MSG_MOD(extack, "Can't find RIF");
> -                       return -EEXIST;
> -               }
> +               if (!re)
> +                       return 0;
>                 prestera_rif_entry_destroy(port->sw, re);
>                 dev_put(port_dev);
>                 break;
>
> [3]
> diff --git a/net/mac80211/main.c b/net/mac80211/main.c
> index 90d295cc364f..0e7a60dd1d8d 100644
> --- a/net/mac80211/main.c
> +++ b/net/mac80211/main.c
> @@ -588,9 +588,7 @@ static int ieee80211_ifa_changed(struct notifier_block *nb,
>         if (sdata->vif.type != NL80211_IFTYPE_STATION)
>                 return NOTIFY_DONE;
>
> -       idev = __in_dev_get_rtnl(sdata->dev);
> -       if (!idev)
> -               return NOTIFY_DONE;
> +       idev = ifa->ifa_dev;
>
>         ifmgd = &sdata->u.mgd;

Thanks for the review comments; I will update prestera and ieee80211,
as well as go through other listeners to confirm the sequence and send
out stacked patches as suggested.

Thanks,

Yuyang