iwlegacy: do not nulify il->vif on reset

This il->vif is dereferenced in different part of iwlegacy code, so do
not nullify it. This should fix random crashes observed in companion
with microcode errors i.e. crash in il3945_config_ap().

Additionally this should address also
WARNING: at drivers/net/wireless/iwlegacy/common.c:4656 il_mac_remove_interface
at least one of the possible reasons of that warning.

Cc: stable@vger.kernel.org
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlegacy/3945-mac.c

@@ -2673,8 +2673,6 @@ il3945_bg_restart(struct work_struct *data)
 
 	if (test_and_clear_bit(S_FW_ERROR, &il->status)) {
 		mutex_lock(&il->mutex);
-		/* FIXME: vif can be dereferenced */
-		il->vif = NULL;
 		il->is_open = 0;
 		mutex_unlock(&il->mutex);
 		il3945_down(il);

drivers/net/wireless/iwlegacy/4965-mac.c

@@ -5651,8 +5651,6 @@ il4965_bg_restart(struct work_struct *data)
 
 	if (test_and_clear_bit(S_FW_ERROR, &il->status)) {
 		mutex_lock(&il->mutex);
-		/* FIXME: do we dereference vif without mutex locked ? */
-		il->vif = NULL;
 		il->is_open = 0;
 
 		__il4965_down(il);

drivers/net/wireless/iwlegacy/common.c

@@ -4508,6 +4508,7 @@ il_mac_add_interface(struct ieee80211_hw *hw, struct ieee80211_vif *vif)
 {
 	struct il_priv *il = hw->priv;
 	int err;
+	bool reset;
 
 	mutex_lock(&il->mutex);
 	D_MAC80211("enter: type %d, addr %pM\n", vif->type, vif->addr);
@@ -4518,7 +4519,12 @@ il_mac_add_interface(struct ieee80211_hw *hw, struct ieee80211_vif *vif)
 		goto out;
 	}
 
-	if (il->vif) {
+	/*
+	 * We do not support multiple virtual interfaces, but on hardware reset
+	 * we have to add the same interface again.
+	 */
+	reset = (il->vif == vif);
+	if (il->vif && !reset) {
 		err = -EOPNOTSUPP;
 		goto out;
 	}
@@ -4528,8 +4534,11 @@ il_mac_add_interface(struct ieee80211_hw *hw, struct ieee80211_vif *vif)
 
 	err = il_set_mode(il);
 	if (err) {
-		il->vif = NULL;
-		il->iw_mode = NL80211_IFTYPE_STATION;
+		IL_WARN("Fail to set mode %d\n", vif->type);
+		if (!reset) {
+			il->vif = NULL;
+			il->iw_mode = NL80211_IFTYPE_STATION;
+		}
 	}
 
 out: