libertas: ensure we clean up a scan request properly

Commit 2e30168b ("libertas: terminate scan when stopping interface")
adds cleanup code to lbs_eth_stop to call cfg80211_scan_done if there's
an outstanding cfg80211_scan_request.  However, it assumes that the
scan request was allocated via the cfg80211 stack.  Libertas has
its own internal allocation method, kept track of with
priv->internal_scan.  This doesn't set scan_req->wiphy, amongst other
things, which results in hitting a BUG() when we call cfg80211_scan_done
on the request.

This provides a function to take care of the low-level scan_req cleanup
details.  We simply call that to deal with finishing up scan requests.

The bug we were hitting was:

[  964.321495] kernel BUG at net/wireless/core.h:87!
[  964.329970] Unable to handle kernel NULL pointer dereference at virtual address 00000000
[  964.341963] pgd = dcf80000
...
[  964.849998] 9fe0: 00000000 beb417b8 4018e280 401e822c 60000010 00000004 00000000 00000000
[  964.865007] [<c003104c>] (__bug+0x1c/0x28) from [<c0384ffc>] (cfg80211_scan_done+0x54/0x6c)
[  964.895324] [<c0384ffc>] (cfg80211_scan_done+0x54/0x6c) from [<bf028bac>] (lbs_eth_stop+0x10c/0x188 [libertas])
[  964.895324] [<bf028bac>] (lbs_eth_stop+0x10c/0x188 [libertas]) from [<c03002a0>] (__dev_close_many+0x94/0xc4)
[  964.918995] [<c03002a0>] (__dev_close_many+0x94/0xc4) from [<c030037c>] (dev_close_many+0x78/0xe0)

Signed-off-by: Andres Salomon <dilinger@queued.net>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas/cfg.c

@@ -728,15 +728,9 @@ static void lbs_scan_worker(struct work_struct *work)
 		le16_to_cpu(scan_cmd->hdr.size),
 		lbs_ret_scan, 0);
 
-	if (priv->scan_channel >= priv->scan_req->n_channels) {
+	if (priv->scan_channel >= priv->scan_req->n_channels)
 		/* Mark scan done */
-		if (priv->internal_scan)
-			kfree(priv->scan_req);
-		else
-			cfg80211_scan_done(priv->scan_req, false);
-
-		priv->scan_req = NULL;
-	}
+		lbs_scan_done(priv);
 
 	/* Restart network */
 	if (carrier)
@@ -774,6 +768,21 @@ static void _internal_start_scan(struct lbs_private *priv, bool internal,
 	lbs_deb_leave(LBS_DEB_CFG80211);
 }
 
+/*
+ * Clean up priv->scan_req.  Should be used to handle the allocation details.
+ */
+void lbs_scan_done(struct lbs_private *priv)
+{
+	WARN_ON(!priv->scan_req);
+
+	if (priv->internal_scan)
+		kfree(priv->scan_req);
+	else
+		cfg80211_scan_done(priv->scan_req, false);
+
+	priv->scan_req = NULL;
+}
+
 static int lbs_cfg_scan(struct wiphy *wiphy,
 	struct net_device *dev,
 	struct cfg80211_scan_request *request)

drivers/net/wireless/libertas/cfg.h

@@ -16,6 +16,7 @@ int lbs_reg_notifier(struct wiphy *wiphy,
 void lbs_send_disconnect_notification(struct lbs_private *priv);
 void lbs_send_mic_failureevent(struct lbs_private *priv, u32 event);
 
+void lbs_scan_done(struct lbs_private *priv);
 void lbs_scan_deinit(struct lbs_private *priv);
 int lbs_disconnect(struct lbs_private *priv, u16 reason);
 

drivers/net/wireless/libertas/main.c

@@ -255,10 +255,8 @@ static int lbs_eth_stop(struct net_device *dev)
 
 	lbs_update_mcast(priv);
 	cancel_delayed_work_sync(&priv->scan_work);
-	if (priv->scan_req) {
-		cfg80211_scan_done(priv->scan_req, false);
-		priv->scan_req = NULL;
-	}
+	if (priv->scan_req)
+		lbs_scan_done(priv);
 
 	netif_carrier_off(priv->dev);