Return-Path: Message-ID: <5434300C.6000602@xsilon.com> Date: Tue, 07 Oct 2014 19:25:16 +0100 From: Martin Townsend MIME-Version: 1.0 To: Alexander Aring , Martin Townsend CC: linux-bluetooth@vger.kernel.org, linux-wpan@vger.kernel.org, marcel@holtmann.org, jukka.rissanen@linux.intel.com Subject: Re: [PATCH bluetooth-next] 6lowpan: Use pskb_expand_head in IPHC decompression. References: <1412696037-25111-1-git-send-email-martin.townsend@xsilon.com> <1412696037-25111-2-git-send-email-martin.townsend@xsilon.com> <20141007161420.GA2216@omega> In-Reply-To: <20141007161420.GA2216@omega> Content-Type: text/plain; charset=utf-8; format=flowed List-ID: Hi Alex, On 07/10/14 17:14, Alexander Aring wrote: > Hi Martin, > > On Tue, Oct 07, 2014 at 04:33:57PM +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 | 53 ++++++++++++++++++++++--------------------- >> net/bluetooth/6lowpan.c | 19 ++++++++++++---- >> net/ieee802154/6lowpan_rtnl.c | 13 +++++++++++ >> 3 files changed, 55 insertions(+), 30 deletions(-) >> >> diff --git a/net/6lowpan/iphc.c b/net/6lowpan/iphc.c >> index 142eef5..fa8f348 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); >> + kfree_skb(skb); >> > I know what before but "consume_skb" agreed. >> return stat; >> } >> @@ -460,7 +452,6 @@ 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; >> >> if (uncompress_udp_header(skb, &uh)) >> goto drop; >> @@ -468,14 +459,15 @@ 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) < sizeof(struct udphdr) + sizeof(hdr)) { >> + int n = sizeof(struct udphdr) + sizeof(hdr); >> + >> + err = pskb_expand_head(skb, n, 0, GFP_ATOMIC); > replace n with constant value "sizeof(struct udphdr) + sizeof(hdr)". ok, I was only trying to make the code more readable here instead of having the calculation split over 2 lines. Actually what is the coding style for this case? or could I use a #define and then I could use it in the if statement above and well as the pskb_expand_head? >> + if (unlikely(err)) { >> + kfree_skb(skb); >> + return err; >> + } >> + } >> >> skb_push(skb, sizeof(struct udphdr)); >> skb_reset_transport_header(skb); >> @@ -485,6 +477,15 @@ 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); >> + > remove whitespace ok >> + if (unlikely(err)) { >> + kfree_skb(skb); >> + return err; >> + } >> + } >> } >> >> hdr.payload_len = htons(skb->len); >> diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c >> index c2e0d14..ab51e16 100644 >> --- a/net/bluetooth/6lowpan.c >> +++ b/net/bluetooth/6lowpan.c >> @@ -343,13 +343,24 @@ 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 */ >> + if (skb_cloned(skb)) { > marker > >> + struct sk_buff *new; >> + int new_headroom = sizeof(struct ipv6hdr) + >> + sizeof(struct udphdr); >> + >> + new = skb_copy_expand(skb, new_headroom, >> + skb_tailroom(skb), GFP_ATOMIC); >> + if (!new) >> + goto drop; >> + consume_skb(skb); >> + skb = new; >> + } >> + >> switch (skb->data[0] & 0xe0) { >> case LOWPAN_DISPATCH_IPHC: /* ipv6 datagram */ >> - local_skb = skb_clone(skb, GFP_ATOMIC); >> - if (!local_skb) >> - goto drop; >> >> - ret = process_data(local_skb, dev, chan); >> + ret = process_data(skb, dev, chan); >> if (ret != NET_RX_SUCCESS) >> goto drop; >> >> diff --git a/net/ieee802154/6lowpan_rtnl.c b/net/ieee802154/6lowpan_rtnl.c >> index c7e07b8..2ccea84 100644 >> --- a/net/ieee802154/6lowpan_rtnl.c >> +++ b/net/ieee802154/6lowpan_rtnl.c >> @@ -537,6 +537,19 @@ static int lowpan_rcv(struct sk_buff *skb, struct net_device *dev, >> if (ret == NET_RX_DROP) >> goto drop; >> } else { >> + /* Decompression may use pskb_expand_head, ensure skb unique */ >> + if (skb_cloned(skb)) { > At this point: > > First: > > this SHOULD be always true in this function, but it doesn't. This is a > complicated issue inside of mac802154. I will ack this, but for the > rework we need to remove this again. Means: Currently I am fine with > this change. That's the intention, once you're rework is in place this can be removed. > We _should_ do it inside the deliver function for multiple interface, > normally we need something like this at mac802154 layer [0]. It's simple > complete broken at current mac802154 mainline state. We set the skb->dev > for only one skb struct and we need to clone it before for each interface... > then we can touch skb->dev again. So multiple interface is... better not use > that. :-) > > Funny at monitor rx function somebody implement a skb_clone before. > > > Second: > > I don't know why this is here, before evaluate the dispatch. If we > receive LOWPAN_DISPATCH_FRAGN we don't need headroom for ipv6hdr/udphdr. > > I think we only need this headroom for uncompression and this is for the > LOWPAN_DISPATCH_IPHC case. But above, see "marker" you do the same > thing again. I mean here we always add room for sizeof(struct ipv6hdr) > + sizeof(struct udphdr), doesn't matter if next header compression is set. > > And above at "marker" we do the same thing. Also do here always a ... + > sizeof(struct udphdr) doesn't fit together with the comming next header > compression framework, which needs to evaluate the nhc id to get the > right next header size which is necessary for the headroom. > > I can only imaging why you doing this here, because it is necessary for > doing the FRAG1 uncompression on the fly stuff, maybe this is some reason > why this is here. But it's not necessary for FRAGN. As it's temporary code is it ok to leave it? >> + struct sk_buff *new; >> + int new_headroom = sizeof(struct ipv6hdr) + >> + sizeof(struct udphdr); >> + >> + new = skb_copy_expand(skb, new_headroom, >> + skb_tailroom(skb), GFP_ATOMIC); >> + if (!new) >> + goto drop_skb; >> + consume_skb(skb); >> + skb = new; >> + } >> switch (skb->data[0] & 0xe0) { >> case LOWPAN_DISPATCH_IPHC: /* ipv6 datagram */ >> ret = process_data(skb, &hdr); > - Alex > > [0] https://github.com/linux-wpan/linux-wpan-next/blob/wpan_rework_rfc/net/mac802154/rx.c#L2 - Martin.