mac80211: keep lock when calling __ieee80211_scan_completed()

We are taking local->mtx inside __ieee80211_scan_completed(), but just
before call to that function we drop the lock. Dropping/taking lock is not
good, because can lead to hard to understand race conditions.

Patch split scan_completed() code into two functions, first must be called
with local->mtx taken and second without it.
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/scan.c

@@ -249,12 +249,12 @@ static bool ieee80211_prep_hw_scan(struct ieee80211_local *local)
 	return true;
 }
 
-static void __ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted)
+static bool __ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted,
+				       bool was_hw_scan)
 {
 	struct ieee80211_local *local = hw_to_local(hw);
-	bool was_hw_scan;
 
-	mutex_lock(&local->mtx);
+	lockdep_assert_held(&local->mtx);
 
 	/*
 	 * It's ok to abort a not-yet-running scan (that
@@ -265,17 +265,13 @@ static void __ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted)
 	if (WARN_ON(!local->scanning && !aborted))
 		aborted = true;
 
-	if (WARN_ON(!local->scan_req)) {
-		mutex_unlock(&local->mtx);
-		return;
-	}
+	if (WARN_ON(!local->scan_req))
+		return false;
 
-	was_hw_scan = test_bit(SCAN_HW_SCANNING, &local->scanning);
 	if (was_hw_scan && !aborted && ieee80211_prep_hw_scan(local)) {
 		ieee80211_queue_delayed_work(&local->hw,
 					     &local->scan_work, 0);
-		mutex_unlock(&local->mtx);
-		return;
+		return false;
 	}
 
 	kfree(local->hw_scan_req);
@@ -289,23 +285,25 @@ static void __ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted)
 	local->scanning = 0;
 	local->scan_channel = NULL;
 
-	/* we only have to protect scan_req and hw/sw scan */
-	mutex_unlock(&local->mtx);
+	return true;
+}
 
-	ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_CHANNEL);
-	if (was_hw_scan)
-		goto done;
+static void __ieee80211_scan_completed_finish(struct ieee80211_hw *hw,
+					      bool was_hw_scan)
+{
+	struct ieee80211_local *local = hw_to_local(hw);
 
+	ieee80211_hw_config(local, IEEE80211_CONF_CHANGE_CHANNEL);
+	if (!was_hw_scan) {
 		ieee80211_configure_filter(local);
-
 		drv_sw_scan_complete(local);
-
 		ieee80211_offchannel_return(local, true);
+	}
 
- done:
 	mutex_lock(&local->mtx);
 	ieee80211_recalc_idle(local);
 	mutex_unlock(&local->mtx);
+
 	ieee80211_mlme_notify_scan_completed(local);
 	ieee80211_ibss_notify_scan_completed(local);
 	ieee80211_mesh_notify_scan_completed(local);
@@ -366,6 +364,8 @@ static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
 	struct ieee80211_local *local = sdata->local;
 	int rc;
 
+	lockdep_assert_held(&local->mtx);
+
 	if (local->scan_req)
 		return -EBUSY;
 
@@ -447,7 +447,7 @@ ieee80211_scan_get_channel_time(struct ieee80211_channel *chan)
 	return IEEE80211_PROBE_DELAY + IEEE80211_CHANNEL_TIME;
 }
 
-static int ieee80211_scan_state_decision(struct ieee80211_local *local,
+static void ieee80211_scan_state_decision(struct ieee80211_local *local,
 					  unsigned long *next_delay)
 {
 	bool associated = false;
@@ -458,12 +458,6 @@ static int ieee80211_scan_state_decision(struct ieee80211_local *local,
 	struct ieee80211_sub_if_data *sdata;
 	struct ieee80211_channel *next_chan;
 
-	/* if no more bands/channels left, complete scan and advance to the idle state */
-	if (local->scan_channel_idx >= local->scan_req->n_channels) {
-		__ieee80211_scan_completed(&local->hw, false);
-		return 1;
-	}
-
 	/*
 	 * check if at least one STA interface is associated,
 	 * check if at least one STA interface has pending tx frames
@@ -535,7 +529,6 @@ static int ieee80211_scan_state_decision(struct ieee80211_local *local,
 	}
 
 	*next_delay = 0;
-	return 0;
 }
 
 static void ieee80211_scan_state_leave_oper_channel(struct ieee80211_local *local,
@@ -651,7 +644,7 @@ void ieee80211_scan_work(struct work_struct *work)
 		container_of(work, struct ieee80211_local, scan_work.work);
 	struct ieee80211_sub_if_data *sdata = local->scan_sdata;
 	unsigned long next_delay = 0;
-	bool aborted;
+	bool aborted, hw_scan, finish;
 
 	mutex_lock(&local->mtx);
 
@@ -704,8 +697,12 @@ void ieee80211_scan_work(struct work_struct *work)
 	do {
 		switch (local->next_scan_state) {
 		case SCAN_DECISION:
-			if (ieee80211_scan_state_decision(local, &next_delay))
-				return;
+			/* if no more bands/channels left, complete scan */
+			if (local->scan_channel_idx >= local->scan_req->n_channels) {
+				aborted = false;
+				goto out_complete;
+			}
+			ieee80211_scan_state_decision(local, &next_delay);
 			break;
 		case SCAN_SET_CHANNEL:
 			ieee80211_scan_state_set_channel(local, &next_delay);
@@ -726,8 +723,11 @@ void ieee80211_scan_work(struct work_struct *work)
 	return;
 
 out_complete:
+	hw_scan = test_bit(SCAN_HW_SCANNING, &local->scanning);
+	finish = __ieee80211_scan_completed(&local->hw, aborted, hw_scan);
 	mutex_unlock(&local->mtx);
-	__ieee80211_scan_completed(&local->hw, aborted);
+	if (finish)
+		__ieee80211_scan_completed_finish(&local->hw, hw_scan);
 	return;
 
 out:
@@ -796,6 +796,7 @@ int ieee80211_request_internal_scan(struct ieee80211_sub_if_data *sdata,
 void ieee80211_scan_cancel(struct ieee80211_local *local)
 {
 	bool abortscan;
+	bool finish = false;
 
 	cancel_delayed_work_sync(&local->scan_work);
 
@@ -806,8 +807,10 @@ void ieee80211_scan_cancel(struct ieee80211_local *local)
 	mutex_lock(&local->mtx);
 	abortscan = test_bit(SCAN_SW_SCANNING, &local->scanning) ||
 		    (!local->scanning && local->scan_req);
+	if (abortscan)
+		finish = __ieee80211_scan_completed(&local->hw, true, false);
 	mutex_unlock(&local->mtx);
 
-	if (abortscan)
-		__ieee80211_scan_completed(&local->hw, true);
+	if (finish)
+		__ieee80211_scan_completed_finish(&local->hw, false);
 }