staging: wfx: fix RCU usage in wfx_join_finalize()

Access to sta->ht_cap is protected by RCU. However,
hif_set_association_mode() may sleep, so it can't be called in RCU.

This patch fix this behavior by handling sta and its RCU directly from
function hif_set_association_mode().

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Fixes: d001490 ("staging: wfx: fix RCU usage")
Link: https://lore.kernel.org/r/20200310101356.182818-5-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/hif_tx_mib.h

@@ -191,10 +191,10 @@ static inline int hif_set_block_ack_policy(struct wfx_vif *wvif,
 }
 
 static inline int hif_set_association_mode(struct wfx_vif *wvif,
-					   struct ieee80211_bss_conf *info,
-					   struct ieee80211_sta_ht_cap *ht_cap)
+					   struct ieee80211_bss_conf *info)
 {
 	int basic_rates = wfx_rate_mask_to_hw(wvif->wdev, info->basic_rates);
+	struct ieee80211_sta *sta = NULL;
 	struct hif_mib_set_association_mode val = {
 		.preambtype_use = 1,
 		.mode = 1,
@@ -204,12 +204,17 @@ static inline int hif_set_association_mode(struct wfx_vif *wvif,
 		.basic_rate_set = cpu_to_le32(basic_rates)
 	};
 
+	rcu_read_lock(); // protect sta
+	if (info->bssid && !info->ibss_joined)
+		sta = ieee80211_find_sta(wvif->vif, info->bssid);
+
 	// FIXME: it is strange to not retrieve all information from bss_info
-	if (ht_cap && ht_cap->ht_supported) {
-		val.mpdu_start_spacing = ht_cap->ampdu_density;
+	if (sta && sta->ht_cap.ht_supported) {
+		val.mpdu_start_spacing = sta->ht_cap.ampdu_density;
 		if (!(info->ht_operation_mode & IEEE80211_HT_OP_MODE_NON_GF_STA_PRSNT))
-			val.greenfield = !!(ht_cap->cap & IEEE80211_HT_CAP_GRN_FLD);
+			val.greenfield = !!(sta->ht_cap.cap & IEEE80211_HT_CAP_GRN_FLD);
 	}
+	rcu_read_unlock();
 
 	return hif_write_mib(wvif->wdev, wvif->id,
 			     HIF_MIB_ID_SET_ASSOCIATION_MODE, &val, sizeof(val));

drivers/staging/wfx/sta.c

@@ -691,6 +691,7 @@ static void wfx_join_finalize(struct wfx_vif *wvif,
 			wfx_rate_mask_to_hw(wvif->wdev, sta->supp_rates[wvif->channel->band]);
 	else
 		wvif->bss_params.operational_rate_set = -1;
+	rcu_read_unlock();
 	if (sta &&
 	    info->ht_operation_mode & IEEE80211_HT_OP_MODE_NON_GF_STA_PRSNT)
 		hif_dual_cts_protection(wvif, true);
@@ -703,8 +704,7 @@ static void wfx_join_finalize(struct wfx_vif *wvif,
 	wvif->bss_params.beacon_lost_count = 20;
 	wvif->bss_params.aid = info->aid;
 
-	hif_set_association_mode(wvif, info, sta ? &sta->ht_cap : NULL);
-	rcu_read_unlock();
+	hif_set_association_mode(wvif, info);
 
 	if (!info->ibss_joined) {
 		hif_keep_alive_period(wvif, 30 /* sec */);