Commit ceaa7141 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

inet: implement lockless IP_MTU_DISCOVER 



inet->pmtudisc can be read locklessly.

Implement proper lockless reads and writes to inet->pmtudisc

ip_sock_set_mtu_discover() can now be called from arbitrary
contexts.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarDavid Ahern <dsahern@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c9746e6a

include/net/ip.h

+8 −5
Original line number Diff line number Diff line
@@ -434,19 +434,22 @@ int ip_dont_fragment(const struct sock *sk, const struct dst_entry *dst) 


static inline bool ip_sk_accept_pmtu(const struct sock *sk)

{

	return inet_sk(sk)->pmtudisc != IP_PMTUDISC_INTERFACE &&

	       inet_sk(sk)->pmtudisc != IP_PMTUDISC_OMIT;

	u8 pmtudisc = READ_ONCE(inet_sk(sk)->pmtudisc);



	return pmtudisc != IP_PMTUDISC_INTERFACE &&

	       pmtudisc != IP_PMTUDISC_OMIT;

}



static inline bool ip_sk_use_pmtu(const struct sock *sk)

{

	return inet_sk(sk)->pmtudisc < IP_PMTUDISC_PROBE;

	return READ_ONCE(inet_sk(sk)->pmtudisc) < IP_PMTUDISC_PROBE;

}



static inline bool ip_sk_ignore_df(const struct sock *sk)

{

	return inet_sk(sk)->pmtudisc < IP_PMTUDISC_DO ||

	       inet_sk(sk)->pmtudisc == IP_PMTUDISC_OMIT;

	u8 pmtudisc = READ_ONCE(inet_sk(sk)->pmtudisc);



	return pmtudisc < IP_PMTUDISC_DO || pmtudisc == IP_PMTUDISC_OMIT;

}



static inline unsigned int ip_dst_mtu_maybe_forward(const struct dst_entry *dst,

net/ipv4/ip_output.c

+4 −3
Original line number Diff line number Diff line
@@ -1387,8 +1387,8 @@ struct sk_buff *__ip_make_skb(struct sock *sk, 
	struct ip_options *opt = NULL;

	struct rtable *rt = (struct rtable *)cork->dst;

	struct iphdr *iph;

	u8 pmtudisc, ttl;

	__be16 df = 0;

	__u8 ttl;



	skb = __skb_dequeue(queue);

	if (!skb)
@@ -1418,8 +1418,9 @@ struct sk_buff *__ip_make_skb(struct sock *sk, 
	/* DF bit is set when we want to see DF on outgoing frames.

	 * If ignore_df is set too, we still allow to fragment this frame

	 * locally. */

	if (inet->pmtudisc == IP_PMTUDISC_DO ||

	    inet->pmtudisc == IP_PMTUDISC_PROBE ||

	pmtudisc = READ_ONCE(inet->pmtudisc);

	if (pmtudisc == IP_PMTUDISC_DO ||

	    pmtudisc == IP_PMTUDISC_PROBE ||

	    (skb->len <= dst_mtu(&rt->dst) &&

	     ip_dont_fragment(sk, &rt->dst)))

		df = htons(IP_DF);

net/ipv4/ip_sockglue.c

+6 −11
Original line number Diff line number Diff line
@@ -622,9 +622,7 @@ int ip_sock_set_mtu_discover(struct sock *sk, int val) 
{

	if (val < IP_PMTUDISC_DONT || val > IP_PMTUDISC_OMIT)

		return -EINVAL;

	lock_sock(sk);

	inet_sk(sk)->pmtudisc = val;

	release_sock(sk);

	WRITE_ONCE(inet_sk(sk)->pmtudisc, val);

	return 0;

}

EXPORT_SYMBOL(ip_sock_set_mtu_discover);
@@ -1050,6 +1048,8 @@ int do_ip_setsockopt(struct sock *sk, int level, int optname, 
			return -EINVAL;

		WRITE_ONCE(inet->mc_ttl, val);

		return 0;

	case IP_MTU_DISCOVER:

		return ip_sock_set_mtu_discover(sk, val);

	}



	err = 0;
@@ -1107,11 +1107,6 @@ int do_ip_setsockopt(struct sock *sk, int level, int optname, 
	case IP_TOS:	/* This sets both TOS and Precedence */

		__ip_sock_set_tos(sk, val);

		break;

	case IP_MTU_DISCOVER:

		if (val < IP_PMTUDISC_DONT || val > IP_PMTUDISC_OMIT)

			goto e_inval;

		inet->pmtudisc = val;

		break;

	case IP_UNICAST_IF:

	{

		struct net_device *dev = NULL;
@@ -1595,6 +1590,9 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname, 
	case IP_MULTICAST_TTL:

		val = READ_ONCE(inet->mc_ttl);

		goto copyval;

	case IP_MTU_DISCOVER:

		val = READ_ONCE(inet->pmtudisc);

		goto copyval;

	}



	if (needs_rtnl)
@@ -1634,9 +1632,6 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname, 
	case IP_TOS:

		val = inet->tos;

		break;

	case IP_MTU_DISCOVER:

		val = inet->pmtudisc;

		break;

	case IP_MTU:

	{

		struct dst_entry *dst;

net/ipv4/ping.c

+1 −1
Original line number Diff line number Diff line
@@ -551,7 +551,7 @@ void ping_err(struct sk_buff *skb, int offset, u32 info) 
		case ICMP_DEST_UNREACH:

			if (code == ICMP_FRAG_NEEDED) { /* Path MTU discovery */

				ipv4_sk_update_pmtu(skb, sk, info);

				if (inet_sock->pmtudisc != IP_PMTUDISC_DONT) {

				if (READ_ONCE(inet_sock->pmtudisc) != IP_PMTUDISC_DONT) {

					err = EMSGSIZE;

					harderr = 1;

					break;

net/ipv4/raw.c

+1 −1
Original line number Diff line number Diff line
@@ -239,7 +239,7 @@ static void raw_err(struct sock *sk, struct sk_buff *skb, u32 info) 
		if (code > NR_ICMP_UNREACH)

			break;

		if (code == ICMP_FRAG_NEEDED) {

			harderr = inet->pmtudisc != IP_PMTUDISC_DONT;

			harderr = READ_ONCE(inet->pmtudisc) != IP_PMTUDISC_DONT;

			err = EMSGSIZE;

		} else {

			err = icmp_err_convert[code].errno;