Re: [PATCH net-next 2/3] net: gro: parse ipv6 ext headers without frag0
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: 2023-12-26 21:59:49
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linux-kselftest, lkml
Richard Gobert wrote:
quoted hunk ↗ jump to hunk
This commit utilizes a new helper function, ipv6_gro_pull_exthdrs, which is used in ipv6_gro_receive to pull ipv6 ext headers instead of ipv6_gso_pull_exthdrs. To use ipv6_gso_pull_exthdr, pskb_pull and __skb_push must be used, and frag0 must be invalidated. This commit removes unnecessary code around the call to ipv6_gso_pull_exthdrs and enables the frag0 fast path in IPv6 packets with ext headers. Signed-off-by: Richard Gobert <redacted> --- net/ipv6/ip6_offload.c | 51 +++++++++++++++++++++++++++++++++--------- 1 file changed, 41 insertions(+), 10 deletions(-)diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c index 0e0b5fed0995..a3b8d9127dbb 100644 --- a/net/ipv6/ip6_offload.c +++ b/net/ipv6/ip6_offload.c@@ -37,6 +37,40 @@ INDIRECT_CALL_L4(cb, f2, f1, head, skb); \ }) +static int ipv6_gro_pull_exthdrs(struct sk_buff *skb, int off, int proto) +{ + const struct net_offload *ops = NULL; + struct ipv6_opt_hdr *opth; + + for (;;) { + int len; + + ops = rcu_dereference(inet6_offloads[proto]); + + if (unlikely(!ops)) + break; + + if (!(ops->flags & INET6_PROTO_GSO_EXTHDR)) + break; + + opth = skb_gro_header(skb, off + 8, off);
When changing this code, it would be great to make it more self documenting. It's not entirely clear what that 8 is based on. sizeof(*opth) is only 2. Probably an optimization to handle the most common extension headers in a single pskb_may_pull? If so, this new code does not have that concern, so can just use sizeof(*opth). Or else add a const int likely_max_opt_hdr_len = 8 or so.
quoted hunk ↗ jump to hunk
+ if (unlikely(!opth)) + break; + + len = ipv6_optlen(opth); + + opth = skb_gro_header(skb, off + len, off); + if (unlikely(!opth)) + break; + proto = opth->nexthdr; + + off += len; + } + + skb_gro_pull(skb, off - skb_network_offset(skb)); + return proto; +} + static int ipv6_gso_pull_exthdrs(struct sk_buff *skb, int proto) { const struct net_offload *ops = NULL;@@ -203,28 +237,25 @@ INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head, goto out; skb_set_network_header(skb, off); - skb_gro_pull(skb, sizeof(*iph)); - skb_set_transport_header(skb, skb_gro_offset(skb)); - flush += ntohs(iph->payload_len) != skb_gro_len(skb); + flush += ntohs(iph->payload_len) != skb->len - hlen; proto = iph->nexthdr; ops = rcu_dereference(inet6_offloads[proto]); if (!ops || !ops->callbacks.gro_receive) { - pskb_pull(skb, skb_gro_offset(skb)); - skb_gro_frag0_invalidate(skb); - proto = ipv6_gso_pull_exthdrs(skb, proto); - skb_gro_pull(skb, -skb_transport_offset(skb)); - skb_reset_transport_header(skb); - __skb_push(skb, skb_gro_offset(skb)); + proto = ipv6_gro_pull_exthdrs(skb, hlen, proto); ops = rcu_dereference(inet6_offloads[proto]); if (!ops || !ops->callbacks.gro_receive) goto out; - iph = ipv6_hdr(skb); + iph = skb_gro_network_header(skb); + } else { + skb_gro_pull(skb, sizeof(*iph)); }
This code is non-obvious and has proven fragile (57ea52a8651). Changes are best as simple as they can be, with ample documentation. My attempt, as arrived at during review: The existing always pulls the IPv6 header and sets the transport offset initially. Then optionally again pulls any extension headers in ipv6_gso_pull_exthdrs and sets the transport offset again on return from that call. The new code adds a small optimization to only pull and set transport offset once. The existing code needs to set skb->data at the start of the first extension header before calling ipv6_gso_pull_exthdrs, and must disable the frag0 optimization because that function uses pskb_may_pull/pskb_pull instead of skb_gro_ helpers. It sets the GRO offset to the inner TCP header with skb_gro_pull and sets the transport header. Then returns skb->data to its position before this block. The new code is much simpler: it does not have to modify skb->data, as all operations are with skb_gro_ helpers. Aside from the small comment above, and suggestion to include something like this summary in the code and/or avoid the extra optimization, Reviewed-by: Willem de Bruijn <willemb@google.com>
+ skb_set_transport_header(skb, skb_gro_offset(skb)); + NAPI_GRO_CB(skb)->proto = proto; flush--; -- 2.36.1