[RFC][PATCH 2/3] TCP/IP Critical socket communication mechanism

[Sridhar Samudrala <sri@us.ibm.com>]

When 'system_in_emergency' flag is set, drop any incoming packets that belong
to non-critical sockets as soon as can determine the destination socket. This
is necessary to prevent incoming non-critical packets to consume memory from
critical page pool.
-----------------------------------------------------------------------------

 include/net/sock.h  |   14 ++++++++++++++
 net/dccp/ipv4.c     |    4 ++++
 net/ipv4/tcp_ipv4.c |    3 +++
 net/ipv4/udp.c      |    9 ++++++++-
 net/ipv6/tcp_ipv6.c |    3 +++
 net/sctp/input.c    |    3 +++
 6 files changed, 35 insertions(+), 1 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 982b4ec..8de8a8b 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1391,4 +1391,18 @@ extern int sysctl_optmem_max;
 extern __u32 sysctl_wmem_default;
 extern __u32 sysctl_rmem_default;

+extern int system_in_emergency;
+
+static inline int emergency_check(struct sock *sk, struct sk_buff *skb)
+{
+	if (system_in_emergency && !(sk->sk_allocation & __GFP_CRITICAL)) {
+		if (net_ratelimit())
+			printk("discarding skb:%p len:%d sk:%p protocol:%d\n",
+                        	skb, skb->len, sk, sk->sk_protocol);
+		return 0;
+	}
+
+	return 1;
+}
+
 #endif	/* _SOCK_H */
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index ca03521..405cdf8 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -1130,6 +1130,10 @@ int dccp_v4_rcv(struct sk_buff *skb)
 		goto no_dccp_socket;
 	}

+	if (!emergency_check(sk, skb)) {
+		goto discard_and_relse;
+	}
+
 	/*
 	 * Step 2:
 	 * 	... or S.state == TIMEWAIT,
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 4d5021e..acfb9a1 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1232,6 +1232,9 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	if (!sk)
 		goto no_tcp_socket;

+	if (!emergency_check(sk, skb))
+		goto discard_and_relse;
+
 process:
 	if (sk->sk_state == TCP_TIME_WAIT)
 		goto do_time_wait;
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 2422a5f..f79cbfd 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1150,7 +1150,14 @@ int udp_rcv(struct sk_buff *skb)
 	sk = udp_v4_lookup(saddr, uh->source, daddr, uh->dest, skb->dev->ifindex);

 	if (sk != NULL) {
-		int ret = udp_queue_rcv_skb(sk, skb);
+		int ret;
+
+		if (!emergency_check(sk, skb)) {
+			sock_put(sk);
+			goto drop;
+		} else
+			ret = udp_queue_rcv_skb(sk, skb);
+
 		sock_put(sk);

 		/* a return value > 0 means to resubmit the input, but
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 62c0e5b..d017181 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1592,6 +1592,9 @@ static int tcp_v6_rcv(struct sk_buff **p
 	if (!sk)
 		goto no_tcp_socket;

+	if (!emergency_check(sk, skb))
+		goto discard_and_relse;
+
 process:
 	if (sk->sk_state == TCP_TIME_WAIT)
 		goto do_time_wait;
diff --git a/net/sctp/input.c b/net/sctp/input.c
index b24ff2c..553365b 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -181,6 +181,9 @@ int sctp_rcv(struct sk_buff *skb)
 	rcvr = asoc ? &asoc->base : &ep->base;
 	sk = rcvr->sk;

+	if (!emergency_check(sk, skb))
+		goto discard_it;
+
 	/*
 	 * If a frame arrives on an interface and the receiving socket is
 	 * bound to another interface, via SO_BINDTODEVICE, treat it as OOTB
-
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