[PATCH v3 net] net: udp: fix Fast/frag0 UDP GRO
From: Alexander Lobakin <hidden>
Date: 2020-11-09 21:15:37
Also in:
lkml
Subsystem:
networking [general], the rest, user datagram protocol (udp) · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Willem de Bruijn
While testing UDP GSO fraglists forwarding through driver that uses
Fast GRO (via napi_gro_frags()), I was observing lots of out-of-order
iperf packets:
[ ID] Interval Transfer Bitrate Jitter
[SUM] 0.0-40.0 sec 12106 datagrams received out-of-order
Simple switch to napi_gro_receive() any other method without frag0
shortcut completely resolved them.
I've found that UDP GRO uses udp_hdr(skb) in its .gro_receive()
callback. While it's probably OK for non-frag0 paths (when all
headers or even the entire frame are already in skb->data), this
inline points to junk when using Fast GRO (napi_gro_frags() or
napi_gro_receive() with only Ethernet header in skb->data and all
the rest in shinfo->frags) and breaks GRO packet compilation and
the packet flow itself.
To support both modes, skb_gro_header_fast() + skb_gro_header_slow()
are typically used. UDP even has an inline helper that makes use of
them, udp_gro_udphdr(). Use that instead of troublemaking udp_hdr()
to get rid of the out-of-order delivers.
Present since the introduction of plain UDP GRO in 5.0-rc1.
Since v2 [1]:
- dropped redundant check introduced in v2 as it's performed right
before (thanks to Eric);
- udp_hdr() switched to data + off for skbs from list (also Eric);
- fixed possible malfunction of {,__}udp{4,6}_lib_lookup_skb() with
Fast/frag0 due to ip{,v6}_hdr() usage (Willem).
Since v1 [2]:
- added a NULL pointer check for "uh" as suggested by Willem.
[1] https://lore.kernel.org/netdev/0eaG8xtbtKY1dEKCTKUBubGiC9QawGgB3tVZtNqVdY@cp4-web-030.plabs.ch (local)
[2] https://lore.kernel.org/netdev/YazU6GEzBdpyZMDMwJirxDX7B4sualpDG68ADZYvJI@cp4-web-034.plabs.ch (local)
Fixes: e20cf8d3f1f7 ("udp: implement GRO for plain UDP sockets.")
Signed-off-by: Alexander Lobakin <redacted>
---
net/ipv4/udp.c | 4 ++--
net/ipv4/udp_offload.c | 9 ++++++---
net/ipv6/udp.c | 4 ++--
3 files changed, 10 insertions(+), 7 deletions(-)
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 09f0a23d1a01..948ddc9a0212 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c@@ -534,7 +534,7 @@ static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb, __be16 sport, __be16 dport, struct udp_table *udptable) { - const struct iphdr *iph = ip_hdr(skb); + const struct iphdr *iph = skb_gro_network_header(skb); return __udp4_lib_lookup(dev_net(skb->dev), iph->saddr, sport, iph->daddr, dport, inet_iif(skb),
@@ -544,7 +544,7 @@ static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb, struct sock *udp4_lib_lookup_skb(struct sk_buff *skb, __be16 sport, __be16 dport) { - const struct iphdr *iph = ip_hdr(skb); + const struct iphdr *iph = skb_gro_network_header(skb); return __udp4_lib_lookup(dev_net(skb->dev), iph->saddr, sport, iph->daddr, dport, inet_iif(skb),
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index e67a66fbf27b..dbc4d17c55e9 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c@@ -366,11 +366,11 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb, static struct sk_buff *udp_gro_receive_segment(struct list_head *head, struct sk_buff *skb) { - struct udphdr *uh = udp_hdr(skb); + struct udphdr *uh = udp_gro_udphdr(skb); struct sk_buff *pp = NULL; struct udphdr *uh2; struct sk_buff *p; - unsigned int ulen; + u32 ulen, off; int ret = 0; /* requires non zero csum, for symmetry with GSO */
@@ -385,6 +385,9 @@ static struct sk_buff *udp_gro_receive_segment(struct list_head *head, NAPI_GRO_CB(skb)->flush = 1; return NULL; } + + off = skb_gro_offset(skb); + /* pull encapsulating udp header */ skb_gro_pull(skb, sizeof(struct udphdr));
@@ -392,7 +395,7 @@ static struct sk_buff *udp_gro_receive_segment(struct list_head *head, if (!NAPI_GRO_CB(p)->same_flow) continue; - uh2 = udp_hdr(p); + uh2 = (void *)p->data + off; /* Match ports only, as csum is always non zero */ if ((*(u32 *)&uh->source != *(u32 *)&uh2->source)) {
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 29d9691359b9..a256ecce76b2 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c@@ -269,7 +269,7 @@ static struct sock *__udp6_lib_lookup_skb(struct sk_buff *skb, __be16 sport, __be16 dport, struct udp_table *udptable) { - const struct ipv6hdr *iph = ipv6_hdr(skb); + const struct ipv6hdr *iph = skb_gro_network_header(skb); return __udp6_lib_lookup(dev_net(skb->dev), &iph->saddr, sport, &iph->daddr, dport, inet6_iif(skb),
@@ -279,7 +279,7 @@ static struct sock *__udp6_lib_lookup_skb(struct sk_buff *skb, struct sock *udp6_lib_lookup_skb(struct sk_buff *skb, __be16 sport, __be16 dport) { - const struct ipv6hdr *iph = ipv6_hdr(skb); + const struct ipv6hdr *iph = skb_gro_network_header(skb); return __udp6_lib_lookup(dev_net(skb->dev), &iph->saddr, sport, &iph->daddr, dport, inet6_iif(skb),
--
2.29.2