mac80211: clean up skb reallocation code

This cleans up the skb reallocation code to avoid problems with
skb->truesize, not resize an skb twice for a single output path
because we didn't expand it enough during the first copy and also
removes the code to further expand it during crypto operations
which will no longer be necessary.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 68 insertions, 29 deletions

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index baa1be0671e..dac44cbd036 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1215,6 +1215,45 @@ retry:
 
 /* device xmit handlers */
 
+static int ieee80211_skb_resize(struct ieee80211_local *local,
+				struct sk_buff *skb,
+				int head_need, bool may_encrypt)
+{
+	int tail_need = 0;
+
+	/*
+	 * This could be optimised, devices that do full hardware
+	 * crypto (including TKIP MMIC) need no tailroom... But we
+	 * have no drivers for such devices currently.
+	 */
+	if (may_encrypt) {
+		tail_need = IEEE80211_ENCRYPT_TAILROOM;
+		tail_need -= skb_tailroom(skb);
+		tail_need = max_t(int, tail_need, 0);
+	}
+
+	if (head_need || tail_need) {
+		/* Sorry. Can't account for this any more */
+		skb_orphan(skb);
+	}
+
+	if (skb_header_cloned(skb))
+		I802_DEBUG_INC(local->tx_expand_skb_head_cloned);
+	else
+		I802_DEBUG_INC(local->tx_expand_skb_head);
+
+	if (pskb_expand_head(skb, head_need, tail_need, GFP_ATOMIC)) {
+		printk(KERN_DEBUG "%s: failed to reallocate TX buffer\n",
+		       wiphy_name(local->hw.wiphy));
+		return -ENOMEM;
+	}
+
+	/* update truesize too */
+	skb->truesize += head_need + tail_need;
+
+	return 0;
+}
+
 int ieee80211_master_start_xmit(struct sk_buff *skb,
 				struct net_device *dev)
 {
@@ -1222,6 +1261,7 @@ int ieee80211_master_start_xmit(struct sk_buff *skb,
 	struct net_device *odev = NULL;
 	struct ieee80211_sub_if_data *osdata;
 	int headroom;
+	bool may_encrypt;
 	int ret;
 
 	if (info->control.ifindex)
@@ -1241,13 +1281,18 @@ int ieee80211_master_start_xmit(struct sk_buff *skb,
 
 	osdata = IEEE80211_DEV_TO_SUB_IF(odev);
 
-	headroom = osdata->local->tx_headroom + IEEE80211_ENCRYPT_HEADROOM;
-	if (skb_headroom(skb) < headroom) {
-		if (pskb_expand_head(skb, headroom, 0, GFP_ATOMIC)) {
-			dev_kfree_skb(skb);
-			dev_put(odev);
-			return 0;
-		}
+	may_encrypt = !(info->flags & IEEE80211_TX_CTL_DO_NOT_ENCRYPT);
+
+	headroom = osdata->local->tx_headroom;
+	if (may_encrypt)
+		headroom += IEEE80211_ENCRYPT_HEADROOM;
+	headroom -= skb_headroom(skb);
+	headroom = max_t(int, 0, headroom);
+
+	if (ieee80211_skb_resize(osdata->local, skb, headroom, may_encrypt)) {
+		dev_kfree_skb(skb);
+		dev_put(odev);
+		return 0;
 	}
 
 	info->control.vif = &osdata->vif;
@@ -1509,32 +1554,26 @@ int ieee80211_subif_start_xmit(struct sk_buff *skb,
 	 * build in headroom in __dev_alloc_skb() (linux/skbuff.h) and
 	 * alloc_skb() (net/core/skbuff.c)
 	 */
-	head_need = hdrlen + encaps_len + meshhdrlen + local->tx_headroom;
-	head_need -= skb_headroom(skb);
+	head_need = hdrlen + encaps_len + meshhdrlen - skb_headroom(skb);
 
-	/* We are going to modify skb data, so make a copy of it if happens to
-	 * be cloned. This could happen, e.g., with Linux bridge code passing
-	 * us broadcast frames. */
+	/*
+	 * So we need to modify the skb header and hence need a copy of
+	 * that. The head_need variable above doesn't, so far, include
+	 * the needed header space that we don't need right away. If we
+	 * can, then we don't reallocate right now but only after the
+	 * frame arrives at the master device (if it does...)
+	 *
+	 * If we cannot, however, then we will reallocate to include all
+	 * the ever needed space. Also, if we need to reallocate it anyway,
+	 * make it big enough for everything we may ever need.
+	 */
 
 	if (head_need > 0 || skb_header_cloned(skb)) {
-#if 0
-		printk(KERN_DEBUG "%s: need to reallocate buffer for %d bytes "
-		       "of headroom\n", dev->name, head_need);
-#endif
-
-		if (skb_header_cloned(skb))
-			I802_DEBUG_INC(local->tx_expand_skb_head_cloned);
-		else
-			I802_DEBUG_INC(local->tx_expand_skb_head);
-		/* Since we have to reallocate the buffer, make sure that there
-		 * is enough room for possible WEP IV/ICV and TKIP (8 bytes
-		 * before payload and 12 after). */
-		if (pskb_expand_head(skb, (head_need > 0 ? head_need + 8 : 8),
-				     12, GFP_ATOMIC)) {
-			printk(KERN_DEBUG "%s: failed to reallocate TX buffer"
-			       "\n", dev->name);
+		head_need += IEEE80211_ENCRYPT_HEADROOM;
+		head_need += local->tx_headroom;
+		head_need = max_t(int, 0, head_need);
+		if (ieee80211_skb_resize(local, skb, head_need, true))
 			goto fail;
-		}
 	}
 
 	if (encaps_data) {