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tcp: dont drop MTU reduction indications

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ICMP messages generated in output path if frame length is bigger than
mtu are actually lost because socket is owned by user (doing the xmit)

One example is the ipgre_tunnel_xmit() calling
icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));

We had a similar case fixed in commit a34a101e1e (ipv6: disable GSO on
sockets hitting dst_allfrag).

Problem of such fix is that it relied on retransmit timers, so short tcp
sessions paid a too big latency increase price.

This patch uses the tcp_release_cb() infrastructure so that MTU
reduction messages (ICMP messages) are not lost, and no extra delay
is added in TCP transmits.

Reported-by: Maciej Żenczykowski <maze@google.com>
Diagnosed-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Nandita Dukkipati <nanditad@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Tore Anderson <tore@fud.no>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2012-07-23 09:48:52 +02:00 committed by David S. Miller
parent c3def943c7
commit 563d34d057
5 changed files with 51 additions and 21 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

6
include/linux/tcp.h
View file

@ -493,6 +493,9 @@ struct tcp_sock {
u32 probe_seq_start;
u32 probe_seq_end;
} mtu_probe;
u32 mtu_info; /* We received an ICMP_FRAG_NEEDED / ICMPV6_PKT_TOOBIG
* while socket was owned by user.
*/
#ifdef CONFIG_TCP_MD5SIG
/* TCP AF-Specific parts; only used by MD5 Signature support so far */
@ -518,6 +521,9 @@ enum tsq_flags {
TCP_TSQ_DEFERRED, /* tcp_tasklet_func() found socket was owned */
TCP_WRITE_TIMER_DEFERRED, /* tcp_write_timer() found socket was owned */
TCP_DELACK_TIMER_DEFERRED, /* tcp_delack_timer() found socket was owned */
TCP_MTU_REDUCED_DEFERRED, /* tcp_v{4|6}_err() could not call
* tcp_v{4|6}_mtu_reduced()
*/
};
static inline struct tcp_sock *tcp_sk(const struct sock *sk)

1
include/net/sock.h
View file

@ -859,6 +859,7 @@ struct proto {
struct sk_buff *skb);
void (*release_cb)(struct sock *sk);
void (*mtu_reduced)(struct sock *sk);
/* Keeping track of sk's, looking them up, and port selection methods. */
void (*hash)(struct sock *sk);

19
net/ipv4/tcp_ipv4.c
View file

@ -275,12 +275,15 @@ failure:
EXPORT_SYMBOL(tcp_v4_connect);
/*
* This routine does path mtu discovery as defined in RFC1191.
* This routine reacts to ICMP_FRAG_NEEDED mtu indications as defined in RFC1191.
* It can be called through tcp_release_cb() if socket was owned by user
* at the time tcp_v4_err() was called to handle ICMP message.
*/
static void do_pmtu_discovery(struct sock *sk, const struct iphdr *iph, u32 mtu)
static void tcp_v4_mtu_reduced(struct sock *sk)
{
struct dst_entry *dst;
struct inet_sock *inet = inet_sk(sk);
u32 mtu = tcp_sk(sk)->mtu_info;
/* We are not interested in TCP_LISTEN and open_requests (SYN-ACKs
* send out by Linux are always <576bytes so they should go through
@ -373,8 +376,12 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
bh_lock_sock(sk);
/* If too many ICMPs get dropped on busy
* servers this needs to be solved differently.
* We do take care of PMTU discovery (RFC1191) special case :
* we can receive locally generated ICMP messages while socket is held.
*/
if (sock_owned_by_user(sk))
if (sock_owned_by_user(sk) &&
type != ICMP_DEST_UNREACH &&
code != ICMP_FRAG_NEEDED)
NET_INC_STATS_BH(net, LINUX_MIB_LOCKDROPPEDICMPS);
if (sk->sk_state == TCP_CLOSE)
@ -409,8 +416,11 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
goto out;
if (code == ICMP_FRAG_NEEDED) { /* PMTU discovery (RFC1191) */
tp->mtu_info = info;
if (!sock_owned_by_user(sk))
do_pmtu_discovery(sk, iph, info);
tcp_v4_mtu_reduced(sk);
else
set_bit(TCP_MTU_REDUCED_DEFERRED, &tp->tsq_flags);
goto out;
}
@ -2596,6 +2606,7 @@ struct proto tcp_prot = {
.sendpage = tcp_sendpage,
.backlog_rcv = tcp_v4_do_rcv,
.release_cb = tcp_release_cb,
.mtu_reduced = tcp_v4_mtu_reduced,
.hash = inet_hash,
.unhash = inet_unhash,
.get_port = inet_csk_get_port,

6
net/ipv4/tcp_output.c
View file

@ -885,7 +885,8 @@ static void tcp_tasklet_func(unsigned long data)
#define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
(1UL << TCP_WRITE_TIMER_DEFERRED) | \
(1UL << TCP_DELACK_TIMER_DEFERRED))
(1UL << TCP_DELACK_TIMER_DEFERRED) | \
(1UL << TCP_MTU_REDUCED_DEFERRED))
/**
* tcp_release_cb - tcp release_sock() callback
* @sk: socket
@ -914,6 +915,9 @@ void tcp_release_cb(struct sock *sk)
if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED))
tcp_delack_timer_handler(sk);
if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED))
sk->sk_prot->mtu_reduced(sk);
}
EXPORT_SYMBOL(tcp_release_cb);

40
net/ipv6/tcp_ipv6.c
View file

@ -315,6 +315,23 @@ failure:
return err;
}
static void tcp_v6_mtu_reduced(struct sock *sk)
{
struct dst_entry *dst;
if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
return;
dst = inet6_csk_update_pmtu(sk, tcp_sk(sk)->mtu_info);
if (!dst)
return;
if (inet_csk(sk)->icsk_pmtu_cookie > dst_mtu(dst)) {
tcp_sync_mss(sk, dst_mtu(dst));
tcp_simple_retransmit(sk);
}
}
static void tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
u8 type, u8 code, int offset, __be32 info)
{
@ -342,7 +359,7 @@ static void tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
}
bh_lock_sock(sk);
if (sock_owned_by_user(sk))
if (sock_owned_by_user(sk) && type != ICMPV6_PKT_TOOBIG)
NET_INC_STATS_BH(net, LINUX_MIB_LOCKDROPPEDICMPS);
if (sk->sk_state == TCP_CLOSE)
@ -371,21 +388,11 @@ static void tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
}
if (type == ICMPV6_PKT_TOOBIG) {
struct dst_entry *dst;
if (sock_owned_by_user(sk))
goto out;
if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
goto out;
dst = inet6_csk_update_pmtu(sk, ntohl(info));
if (!dst)
goto out;
if (inet_csk(sk)->icsk_pmtu_cookie > dst_mtu(dst)) {
tcp_sync_mss(sk, dst_mtu(dst));
tcp_simple_retransmit(sk);
}
tp->mtu_info = ntohl(info);
if (!sock_owned_by_user(sk))
tcp_v6_mtu_reduced(sk);
else
set_bit(TCP_MTU_REDUCED_DEFERRED, &tp->tsq_flags);
goto out;
}
@ -1949,6 +1956,7 @@ struct proto tcpv6_prot = {
.sendpage = tcp_sendpage,
.backlog_rcv = tcp_v6_do_rcv,
.release_cb = tcp_release_cb,
.mtu_reduced = tcp_v6_mtu_reduced,
.hash = tcp_v6_hash,
.unhash = inet_unhash,
.get_port = inet_csk_get_port,