RE: [BUG] wifi: rtw88: WARN_ON storm from rtw_get_channel_group() - 5GHz channel 163 missing from switch

[Ping-Ke Shih <pkshih@realtek.com>]

Luis Albisu <lfa@me.com> wrote:
> Hi,
> 
> This report was generated by Claude Code after it addressed an issue it found on one of my machines.
> 
> It suggested I submit this since it might be of interest.
> 
> Thank you for developing and making this code available and I hope this is helpful!
> 
> Sincerely,
> 
> LFA
> 
> On 6.18.29 an RTL8821AU in monitor mode produces a WARN_ON backtrace on
> every channel hop that lands on 5GHz channel 165 with HT40, at roughly
> 152 warnings per visit. Over a day this wrote 2.8 GB of journal on the
> host and cut log retention from ~15 days to ~1.5. Not fatal, but it
> taints the kernel and buries every other log line.

I think the restriction always presents, right? Or only happens after 6.18.29?

> 
> Hardware / software
> -------------------
> Adapter:  Alfa AWUS036ACS, USB 0bda:0811
>           "Realtek 8812AU/8821AU 802.11ac WLAN Adapter"
> Driver:   rtw88_8821au / rtw88_8821a / rtw88_88xxa / rtw88_usb / rtw88_core
> Kernel:   6.18.29+rpt-rpi-2712 #1 PREEMPT Debian 1:6.18.29-1+rpt1, aarch64
> Machine:  Raspberry Pi 5 Model B Rev 1.0
> Regdom:   country US (DFS-FCC); relevant range (5730 - 5850 @ 80)
> Consumer: Kismet, monitor VIF, channel_hop_speed=1/sec
> 
> Reproduction
> ------------
> Put the adapter in monitor mode and set the channel to 165 with HT40
> (Kismet's linuxwifi source does this automatically as part of its hop
> list). Every such hop emits the backtrace below. Channels 1-11, 36-64,
> 100-144, 149-161 are all clean; only hops involving 165 warn.
> 
> I isolated it by sampling `iw dev wlan1mon info` every 150 ms for 60 s
> and joining the samples to warning timestamps. All 152 warnings in that
> window fell in the two sample windows adjacent to the single visit to
> channel 165. A visit to channel 161 at HT40 in a cycle that did not
> include 165 produced zero warnings, as did every 20 MHz and 80 MHz
> visit to every other channel.
> 
> Removing 165 from the hop list stops it completely: 480 warnings per
> 10 minutes before, 0 across three separate 10-minute windows after.
> 

It looks similar to the one we met before. Please apply [1] to see
if it can avoid the warning, but it also denies the use of certain channels.

[1] https://patchwork.kernel.org/project/linux-wireless/patch/20260413053601.13037-1-pkshih@realtek.com/