Hi Martin,
On Wed, Oct 08, 2014 at 08:35:45AM +0100, Martin Townsend wrote:
> Currently there are potentially 2 skb_copy_expand calls in IPHC
> decompression. This patch replaces this with one call to
> pskb_expand_head. It also checks to see if there is enough headroom
> first to ensure it's only done if necessary.
> As pskb_expand_head must only have one reference the calling code
> now ensures this.
>
> Signed-off-by: Martin Townsend <martin.townsend@xxxxxxxxxx>
> ---
> net/6lowpan/iphc.c | 51 +++++++++++++++++++++----------------------
> net/bluetooth/6lowpan.c | 12 ++++++----
> net/ieee802154/6lowpan_rtnl.c | 5 +++++
> 3 files changed, 38 insertions(+), 30 deletions(-)
>
> diff --git a/net/6lowpan/iphc.c b/net/6lowpan/iphc.c
> index 142eef5..853b4b8 100644
> --- a/net/6lowpan/iphc.c
> +++ b/net/6lowpan/iphc.c
> @@ -174,30 +174,22 @@ static int uncompress_context_based_src_addr(struct sk_buff *skb,
> static int skb_deliver(struct sk_buff *skb, struct ipv6hdr *hdr,
> struct net_device *dev, skb_delivery_cb deliver_skb)
> {
> - struct sk_buff *new;
> int stat;
>
> - new = skb_copy_expand(skb, sizeof(struct ipv6hdr), skb_tailroom(skb),
> - GFP_ATOMIC);
> - kfree_skb(skb);
> -
> - if (!new)
> - return -ENOMEM;
> -
> - skb_push(new, sizeof(struct ipv6hdr));
> - skb_reset_network_header(new);
> - skb_copy_to_linear_data(new, hdr, sizeof(struct ipv6hdr));
> + skb_push(skb, sizeof(struct ipv6hdr));
> + skb_reset_network_header(skb);
> + skb_copy_to_linear_data(skb, hdr, sizeof(struct ipv6hdr));
>
Just a hint, don't do that in this patch or send a patch series.
I would in a future move:
skb_push(skb, sizeof(struct ipv6hdr));
skb_reset_network_header(skb);
skb_copy_to_linear_data(skb, hdr, sizeof(struct ipv6hdr));
into the end of iphc decompression, because we do the same thing for
transport header in iphc decompression.
> - new->protocol = htons(ETH_P_IPV6);
> - new->pkt_type = PACKET_HOST;
> - new->dev = dev;
> + skb->protocol = htons(ETH_P_IPV6);
> + skb->pkt_type = PACKET_HOST;
> + skb->dev = dev;
This we should leave here. Then bluetooth/802.15.4 can set different
things here.
...
> hdr.payload_len = htons(skb->len);
> diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
> index c2e0d14..bd85edf 100644
> --- a/net/bluetooth/6lowpan.c
> +++ b/net/bluetooth/6lowpan.c
> @@ -343,13 +343,17 @@ static int recv_pkt(struct sk_buff *skb, struct net_device *dev,
> kfree_skb(local_skb);
> kfree_skb(skb);
> } else {
> + /* Decompression may use pskb_expand_head, ensure skb unique */
> + skb = skb_unshare(skb, GFP_ATOMIC);
> + if (!skb) {
> + dev->stats.rx_dropped++;
> + return NET_RX_DROP;
> + }
> +
What I meant here in my previous review notes is that kfree_skb(skb);
was correct but in this case we can't do it, we need a temp variable.
skb = skb_unshare(skb, GFP_ATOMIC);
here we lost the skb reference from parameter if failed and I don't see
that skb_unshare free it on failing (maybe I am wrong here).
foo(any name for a tmp skb name, I see a lot of nskb names for a tmp skb
name. Maybe this is a usual name convention) = skb_unshare(skb, GFP_ATOMIC);
Then we don't lost the "skb" parameter reference and can free it with
kfree_skb(skb).
If all is fine we can run a skb = foo.
I think that skb_unshare and the buffer is NOT shared then (skb == foo),
but I am not sure about this. If it's NOT the same then we have some
memory leaking here.
- Alex
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