Re: [PATCH v3 1/3] wifi: rtw88: Move register access from rtw_bf_assoc() outside the RCU

[Sascha Hauer <s.hauer@pengutronix.de>]

On Sun, Jan 08, 2023 at 10:13:22PM +0100, Martin Blumenstingl wrote:
> USB and (upcoming) SDIO support may sleep in the read/write handlers.
> Shrink the RCU critical section so it only cover the call to
> ieee80211_find_sta() and finding the ic_vht_cap/vht_cap based on the
> found station. This moves the chip's BFEE configuration outside the
> rcu_read_lock section and thus prevent "scheduling while atomic" or
> "Voluntary context switch within RCU read-side critical section!"
> warnings when accessing the registers using an SDIO card (which is
> where this issue has been spotted in the real world - but it also
> affects USB cards).

Unfortunately this introduces a regression on my RTW8821CU chip. With
this it constantly looses connection to the AP and reconnects shortly
after:

[  199.771143] wlan0: authenticate with b0:be:76:5e:7b:34
[  201.447301] wlan0: send auth to b0:be:76:5e:7b:34 (try 1/3)
[  201.456789] wlan0: authenticated
[  201.462356] wlan0: associate with b0:be:76:5e:7b:34 (try 1/3)
[  201.477263] wlan0: RX AssocResp from b0:be:76:5e:7b:34 (capab=0x431 status=0 aid=2)
[  201.512995] wlan0: associated
[  213.790399] wlan0: authenticate with b0:be:76:5e:7b:34
[  215.467302] wlan0: send auth to b0:be:76:5e:7b:34 (try 1/3)
[  215.470532] wlan0: authenticated
[  215.490355] wlan0: associate with b0:be:76:5e:7b:34 (try 1/3)
[  215.503777] wlan0: RX AssocResp from b0:be:76:5e:7b:34 (capab=0x431 status=0 aid=2)
[  215.539608] wlan0: associated
[  227.770596] wlan0: authenticate with b0:be:76:5e:7b:34
[  229.443302] wlan0: send auth to b0:be:76:5e:7b:34 (try 1/3)
[  229.451209] wlan0: authenticated
[  229.462487] wlan0: associate with b0:be:76:5e:7b:34 (try 1/3)
[  229.476077] wlan0: RX AssocResp from b0:be:76:5e:7b:34 (capab=0x431 status=0 aid=2)
[  229.513499] wlan0: associated
[  241.738494] wlan0: authenticate with b0:be:76:5e:7b:34
[  243.407301] wlan0: send auth to b0:be:76:5e:7b:34 (try 1/3)
[  243.411207] wlan0: authenticated
[  243.423213] wlan0: associate with b0:be:76:5e:7b:34 (try 1/3)
[  243.439822] wlan0: RX AssocResp from b0:be:76:5e:7b:34 (capab=0x431 status=0 aid=2)
[  243.476731] wlan0: associated

I haven't got any further information yet, I just realized this when I
rebased my own RTW88 bugfix series from v6.2.2 to v6.3-rc4 before
sending it.

RTW8723D and RTW8822CU seem unaffected though.

Sascha

> 
> Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
> Tested-by: Sascha Hauer <s.hauer@pengutronix.de>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
> ---
> v1 -> v2:
> - Added Ping-Ke's Reviewed-by (thank you!)
> 
> v2 -> v3:
> - Added Sascha's Tested-by (thank you!)
> - added "wifi" prefix to the subject and reworded the title accordingly
> 
> 
>  drivers/net/wireless/realtek/rtw88/bf.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/wireless/realtek/rtw88/bf.c b/drivers/net/wireless/realtek/rtw88/bf.c
> index 038a30b170ef..c827c4a2814b 100644
> --- a/drivers/net/wireless/realtek/rtw88/bf.c
> +++ b/drivers/net/wireless/realtek/rtw88/bf.c
> @@ -49,19 +49,23 @@ void rtw_bf_assoc(struct rtw_dev *rtwdev, struct ieee80211_vif *vif,
>  
>  	sta = ieee80211_find_sta(vif, bssid);
>  	if (!sta) {
> +		rcu_read_unlock();
> +
>  		rtw_warn(rtwdev, "failed to find station entry for bss %pM\n",
>  			 bssid);
> -		goto out_unlock;
> +		return;
>  	}
>  
>  	ic_vht_cap = &hw->wiphy->bands[NL80211_BAND_5GHZ]->vht_cap;
>  	vht_cap = &sta->deflink.vht_cap;
>  
> +	rcu_read_unlock();
> +
>  	if ((ic_vht_cap->cap & IEEE80211_VHT_CAP_MU_BEAMFORMEE_CAPABLE) &&
>  	    (vht_cap->cap & IEEE80211_VHT_CAP_MU_BEAMFORMER_CAPABLE)) {
>  		if (bfinfo->bfer_mu_cnt >= chip->bfer_mu_max_num) {
>  			rtw_dbg(rtwdev, RTW_DBG_BF, "mu bfer number over limit\n");
> -			goto out_unlock;
> +			return;
>  		}
>  
>  		ether_addr_copy(bfee->mac_addr, bssid);
> @@ -75,7 +79,7 @@ void rtw_bf_assoc(struct rtw_dev *rtwdev, struct ieee80211_vif *vif,
>  		   (vht_cap->cap & IEEE80211_VHT_CAP_SU_BEAMFORMER_CAPABLE)) {
>  		if (bfinfo->bfer_su_cnt >= chip->bfer_su_max_num) {
>  			rtw_dbg(rtwdev, RTW_DBG_BF, "su bfer number over limit\n");
> -			goto out_unlock;
> +			return;
>  		}
>  
>  		sound_dim = vht_cap->cap &
> @@ -98,9 +102,6 @@ void rtw_bf_assoc(struct rtw_dev *rtwdev, struct ieee80211_vif *vif,
>  
>  		rtw_chip_config_bfee(rtwdev, rtwvif, bfee, true);
>  	}
> -
> -out_unlock:
> -	rcu_read_unlock();
>  }
>  
>  void rtw_bf_init_bfer_entry_mu(struct rtw_dev *rtwdev,
> -- 
> 2.39.0
> 
> 

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |