Re: [PATCH wireless-next 1/2] wifi: mac80211: set band information for NULL packets only for non-MLO stations

[Johannes Berg <johannes@sipsolutions.net>]

On Thu, 2025-11-27 at 19:35 +0530, Suraj P Kizhakkethil wrote:
> Currently, when sending a NULL packet to probe a station, the band
> information is derived from the chanctx_conf in the mac80211 vif's
> bss_conf. However, for MLO, chanctx_conf is not assigned to the vif's
> bss_conf; instead it is assigned on a per-link basis. As a result,
> for MLO, sending a NULL packet to probe will trigger a warning.
> 
> WARNING: net/mac80211/cfg.c:4593 at ieee80211_probe_client+0x1a8/0x1e0 [mac80211], CPU#2: hostapd/241
> Call trace:
>  ieee80211_probe_client+0x1a8/0x1e0 [mac80211] (P)
>  nl80211_probe_client+0xac/0x170 [cfg80211]
>  genl_family_rcv_msg_doit+0xc8/0x134
>  genl_rcv_msg+0x200/0x280
>  netlink_rcv_skb+0x38/0xfc
>  genl_rcv+0x34/0x48
>  netlink_unicast+0x228/0x334
>  netlink_sendmsg+0x158/0x364
>  ____sys_sendmsg+0x1f4/0x21c
>  ___sys_sendmsg+0x98/0xc0
>  __sys_sendmsg+0x74/0xd0
>  __arm64_sys_sendmsg+0x20/0x28
>  invoke_syscall.constprop.0+0x4c/0xd0
>  do_el0_svc+0x3c/0xd0
>  el0_svc+0x28/0xb8
>  el0t_64_sync_handler+0x98/0xdc
>  el0t_64_sync+0x154/0x158
> ---[ end trace 0000000000000000 ]---
> 
> For NULL packets sent to probe stations, set the band information only
> for non-MLD case, since MLD transmissions does not rely on band. For
> MLD connections, set the link ID as unspecified to allow the driver
> to select the appropriate link. The case specific to non-MLO stations
> connected to an MLD AP will be addressed in a follow up patch.

Technically "AP MLD" ;)

But I was more wondering about the use of "MLD connections", which seems
odd to me (vs. "MLO connections")? Connections between MLDs? MLD is an
entity, MLO is the mode of operation?

> +	if (ieee80211_vif_is_mld(&sdata->vif))
> +		info->control.flags |= IEEE80211_TX_CTRL_MLO_LINK_UNSPEC;

I don't see why it should be set conditionally, it should be ignored
anyway by non-MLO drivers? Or maybe if you'd want it zero for t hose
then do that explicitly?

I'm really commenting here because it gets messy in the next patch, see
also there.

johannes