mac80211: fix scan locking wrt. hw scan

Releasing the scan mutex while starting scans
can lead to unexpected things happening, so
we shouldn't do that. Fix that and hold the
mutex across the scan triggering.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/scan.c

@@ -400,19 +400,7 @@ static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
 	else
 		__set_bit(SCAN_SW_SCANNING, &local->scanning);
 
-	/*
-	 * Kicking off the scan need not be protected,
-	 * only the scan variable stuff, since now
-	 * local->scan_req is assigned and other callers
-	 * will abort their scan attempts.
-	 *
-	 * This avoids too many locking dependencies
-	 * so that the scan completed calls have more
-	 * locking freedom.
-	 */
-
 	ieee80211_recalc_idle(local);
-	mutex_unlock(&local->scan_mtx);
 
 	if (local->ops->hw_scan) {
 		WARN_ON(!ieee80211_prep_hw_scan(local));
@@ -420,8 +408,6 @@ static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
 	} else
 		rc = ieee80211_start_sw_scan(local);
 
-	mutex_lock(&local->scan_mtx);
-
 	if (rc) {
 		kfree(local->hw_scan_req);
 		local->hw_scan_req = NULL;