mac80211: Defer tranmission of mesh path errors

Under failure conditions, the mesh stack sends PERR messages to the
previous sender of the failed frame.  This happens in the tx feedback
path, in which the transmission queue lock may be taken.  Avoid a
deadlock by sending the path error via the pending queue.

Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/mesh_hwmp.c

@@ -8,6 +8,7 @@
  */
 
 #include <linux/slab.h>
+#include "wme.h"
 #include "mesh.h"
 
 #ifdef CONFIG_MAC80211_VERBOSE_MHWMP_DEBUG
@@ -202,13 +203,38 @@ static int mesh_path_sel_frame_tx(enum mpath_frame_type action, u8 flags,
 	return 0;
 }
 
+
+/*  Headroom is not adjusted.  Caller should ensure that skb has sufficient
+ *  headroom in case the frame is encrypted. */
+static void prepare_frame_for_deferred_tx(struct ieee80211_sub_if_data *sdata,
+		struct sk_buff *skb)
+{
+	struct ieee80211_local *local = sdata->local;
+	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+
+	skb_set_mac_header(skb, 0);
+	skb_set_network_header(skb, 0);
+	skb_set_transport_header(skb, 0);
+
+	/* Send all internal mgmt frames on VO. Accordingly set TID to 7. */
+	skb_set_queue_mapping(skb, IEEE80211_AC_VO);
+	skb->priority = 7;
+
+	info->control.vif = &sdata->vif;
+	ieee80211_set_qos_hdr(local, skb);
+}
+
 /**
  * mesh_send_path error - Sends a PERR mesh management frame
  *
  * @target: broken destination
  * @target_sn: SN of the broken destination
  * @target_rcode: reason code for this PERR
  * @ra: node this frame is addressed to
+ *
+ * Note: This function may be called with driver locks taken that the driver
+ * also acquires in the TX path.  To avoid a deadlock we don't transmit the
+ * frame directly but add it to the pending queue instead.
  */
 int mesh_path_error_tx(u8 ttl, u8 *target, __le32 target_sn,
 		       __le16 target_rcode, const u8 *ra,
@@ -222,7 +248,7 @@ int mesh_path_error_tx(u8 ttl, u8 *target, __le32 target_sn,
 
 	if (!skb)
 		return -1;
-	skb_reserve(skb, local->hw.extra_tx_headroom);
+	skb_reserve(skb, local->tx_headroom + local->hw.extra_tx_headroom);
 	/* 25 is the size of the common mgmt part (24) plus the size of the
 	 * common action part (1)
 	 */
@@ -263,7 +289,9 @@ int mesh_path_error_tx(u8 ttl, u8 *target, __le32 target_sn,
 	pos += 4;
 	memcpy(pos, &target_rcode, 2);
 
-	ieee80211_tx_skb(sdata, skb);
+	/* see note in function header */
+	prepare_frame_for_deferred_tx(sdata, skb);
+	ieee80211_add_pending_skb(local, skb);
 	return 0;
 }