RE: [PATCH 2/4] rtw88: Configure the registers from rtw_bf_assoc() outside the RCU lock

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

> -----Original Message-----
> From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
> Sent: Wednesday, December 28, 2022 9:36 PM
> To: linux-wireless@vger.kernel.org
> Cc: tony0620emma@gmail.com; kvalo@kernel.org; Ping-Ke Shih <pkshih@realtek.com>; tehuang@realtek.com;
> s.hauer@pengutronix.de; netdev@vger.kernel.org; linux-kernel@vger.kernel.org; Martin Blumenstingl
> <martin.blumenstingl@googlemail.com>
> Subject: [PATCH 2/4] rtw88: Configure the registers from rtw_bf_assoc() outside the RCU lock
> 
> 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).
> 
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>


> ---
>  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