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

[Martin Blumenstingl <martin.blumenstingl@googlemail.com>]

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).

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