Return-Path: Date: Sat, 11 Oct 2014 09:36:22 +0200 From: Alexander Aring To: Martin Townsend Cc: linux-bluetooth@vger.kernel.org, linux-wpan@vger.kernel.org, marcel@holtmann.org, jukka.rissanen@linux.intel.com, Martin Townsend Subject: Re: [PATCH v5 bluetooth-next] 6lowpan: Use pskb_expand_head in IPHC decompression. Message-ID: <20141011073620.GA28500@omega> References: <1412840794-17283-1-git-send-email-martin.townsend@xsilon.com> <1412840794-17283-2-git-send-email-martin.townsend@xsilon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <1412840794-17283-2-git-send-email-martin.townsend@xsilon.com> List-ID: Hi Martin, This is only a summarize what we should now to try to do here for next version. I know... this patch ends in a global debate on principles how we deal with the replacement of 6LoWPAN -> IPv6 header. Current behaviour is more a hack. On Thu, Oct 09, 2014 at 08:46:34AM +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 > --- > net/6lowpan/iphc.c | 51 ++++++++++++++++++++++++------------------------- > net/bluetooth/6lowpan.c | 7 +++++++ > 2 files changed, 32 insertions(+), 26 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)); > > - 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; > > raw_dump_table(__func__, "raw skb data dump before receiving", > - new->data, new->len); > + skb->data, skb->len); > > - stat = deliver_skb(new, dev); > + stat = deliver_skb(skb, dev); > > - kfree_skb(new); > + consume_skb(skb); > > return stat; > } > @@ -460,7 +452,7 @@ int lowpan_process_data(struct sk_buff *skb, struct net_device *dev, > /* UDP data uncompression */ > if (iphc0 & LOWPAN_IPHC_NH_C) { > struct udphdr uh; > - struct sk_buff *new; > + const int needed = sizeof(struct udphdr) + sizeof(hdr); > > if (uncompress_udp_header(skb, &uh)) > goto drop; > @@ -468,14 +460,13 @@ int lowpan_process_data(struct sk_buff *skb, struct net_device *dev, > /* replace the compressed UDP head by the uncompressed UDP > * header > */ > - new = skb_copy_expand(skb, sizeof(struct udphdr), > - skb_tailroom(skb), GFP_ATOMIC); > - kfree_skb(skb); > - > - if (!new) > - return -ENOMEM; > - > - skb = new; > + if (skb_headroom(skb) < needed) { > + err = pskb_expand_head(skb, needed, 0, GFP_ATOMIC); > + if (unlikely(err)) { > + kfree_skb(skb); > + return err; > + } > + } use skb_cow_head here. > > skb_push(skb, sizeof(struct udphdr)); > skb_reset_transport_header(skb); > @@ -485,6 +476,14 @@ int lowpan_process_data(struct sk_buff *skb, struct net_device *dev, > (u8 *)&uh, sizeof(uh)); > > hdr.nexthdr = UIP_PROTO_UDP; > + } else { > + if (skb_headroom(skb) < sizeof(hdr)) { > + err = pskb_expand_head(skb, sizeof(hdr), 0, GFP_ATOMIC); > + if (unlikely(err)) { > + kfree_skb(skb); > + return err; > + } > + } same here. > } > > hdr.payload_len = htons(skb->len); > diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c > index c2e0d14..6643a7c 100644 > --- a/net/bluetooth/6lowpan.c > +++ b/net/bluetooth/6lowpan.c > @@ -343,6 +343,13 @@ 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 so no shared skb's */ > + skb = skb_share_check(skb, GFP_ATOMIC); > + if (!skb) { > + dev->stats.rx_dropped++; > + return NET_RX_DROP; > + } > + I see now that case LOWPAN_DISPATCH_IPHC: runs a "local_skb = skb_clone(skb, GFP_ATOMIC);" and send the local_skb to process_data. So is the share_check really needed? In my opinion there are several things wrong. What bluetooth should do here is: Always run skb = skb_share_check(skb, GFP_ATOMIC); at first of this function. In if (skb->data[0] == LOWPAN_DISPATCH_IPV6): - only run a skb_pull (doesn't change the data buffer, only skb attribute) for the one byte dispatch. - run other things like skb_reset_network_header, etc... -> Currently this works because we run a complete skb_copy_expand here. But this is not needed, we need a clone because we don't modify the data buffer. -> To Jukka: I don't see a skb_pull for the one byte dispatch value? What's happend here? Also IPv6 dispatch is part of rfc4944 and btle 6LoWPAN is only realted to rfc6282 (IPHC). I think you don't need handling for this here. In "case LOWPAN_DISPATCH_IPHC:" we should remove the skb_clone, because this is already handled by "skb_share_check" then. - Alex