[PATCH 1/3] mac80211: fix initialization of skb->cb in ieee80211_subif_start_xmit

[PATCH 1/3] mac80211: fix initialization of skb->cb in ieee80211_subif_start_xmit

[Felix Fietkau]

The change 'mac80211: Fix BUG in pskb_expand_head when transmitting shared skbs'
added a check for copying the skb if it's shared, however the tx info variable
still points at the cb of the old skb

Cc: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
---
 net/mac80211/tx.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 898e864..7d78aca 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1742,7 +1742,7 @@ netdev_tx_t ieee80211_subif_start_xmit(struct sk_buff *skb,
 {
 	struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 	struct ieee80211_local *local = sdata->local;
-	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+	struct ieee80211_tx_info *info;
 	int ret = NETDEV_TX_BUSY, head_need;
 	u16 ethertype, hdrlen,  meshhdrlen = 0;
 	__le16 fc;
@@ -2033,6 +2033,7 @@ netdev_tx_t ieee80211_subif_start_xmit(struct sk_buff *skb,
 	skb_set_network_header(skb, nh_pos);
 	skb_set_transport_header(skb, h_pos);
 
+	info = IEEE80211_SKB_CB(skb);
 	memset(info, 0, sizeof(*info));
 
 	dev->trans_start = jiffies;
-- 
1.7.3.2

[PATCH 2/3] mac80211: skip unnecessary pskb_expand_head calls

[Felix Fietkau]

If the skb is not cloned and we don't need any extra headroom, there
is no point in reallocating the skb head.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
---
 net/mac80211/tx.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 7d78aca..56ae175 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1549,8 +1549,10 @@ static int ieee80211_skb_resize(struct ieee80211_local *local,
 
 	if (skb_header_cloned(skb))
 		I802_DEBUG_INC(local->tx_expand_skb_head_cloned);
-	else
+	else if (head_need || tail_need)
 		I802_DEBUG_INC(local->tx_expand_skb_head);
+	else
+		return 0;
 
 	if (pskb_expand_head(skb, head_need, tail_need, GFP_ATOMIC)) {
 		wiphy_debug(local->hw.wiphy,
-- 
1.7.3.2

[PATCH 3/3] mac80211: fix potentially redundant skb data copying

[Felix Fietkau]

When an skb is shared, it needs to be duplicated, along with its data buffer.
If the skb does not have enough headroom, using skb_copy might cause the data
buffer to be copied twice (once by skb_copy and once by pskb_expand_head).
Fix this by using skb_clone initially and letting ieee80211_skb_resize sort
out the rest.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
---
 net/mac80211/tx.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 56ae175..d484c07 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1939,7 +1939,7 @@ netdev_tx_t ieee80211_subif_start_xmit(struct sk_buff *skb,
 	 */
 	if (skb_shared(skb)) {
 		tmp_skb = skb;
-		skb = skb_copy(skb, GFP_ATOMIC);
+		skb = skb_clone(skb, GFP_ATOMIC);
 		kfree_skb(tmp_skb);
 
 		if (!skb) {
-- 
1.7.3.2

Re: [PATCH 1/3] mac80211: fix initialization of skb->cb in ieee80211_subif_start_xmit

[Helmut Schaa]

Am Samstag, 18. Dezember 2010 schrieb Felix Fietkau:
> The change 'mac80211: Fix BUG in pskb_expand_head when transmitting shared skbs'
> added a check for copying the skb if it's shared, however the tx info variable
> still points at the cb of the old skb
> 
> Cc: Helmut Schaa <helmut.schaa@googlemail.com>
> Signed-off-by: Felix Fietkau <nbd@openwrt.org>

Ah, missed that. Thanks Felix.

Acked-by: Helmut Schaa <helmut.schaa@googlemail.com>

> ---
>  net/mac80211/tx.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index 898e864..7d78aca 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -1742,7 +1742,7 @@ netdev_tx_t ieee80211_subif_start_xmit(struct sk_buff *skb,
>  {
>  	struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
>  	struct ieee80211_local *local = sdata->local;
> -	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
> +	struct ieee80211_tx_info *info;
>  	int ret = NETDEV_TX_BUSY, head_need;
>  	u16 ethertype, hdrlen,  meshhdrlen = 0;
>  	__le16 fc;
> @@ -2033,6 +2033,7 @@ netdev_tx_t ieee80211_subif_start_xmit(struct sk_buff *skb,
>  	skb_set_network_header(skb, nh_pos);
>  	skb_set_transport_header(skb, h_pos);
>  
> +	info = IEEE80211_SKB_CB(skb);
>  	memset(info, 0, sizeof(*info));
>  
>  	dev->trans_start = jiffies;
>