From 946f9eb226c296da0d6c630bdad282ca11d77f60 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 20 May 2015 10:59:02 -0700 Subject: [PATCH] tcp: improve REUSEADDR/NOREUSEADDR cohabitation inet_csk_get_port() randomization effort tends to spread sockets on all the available range (ip_local_port_range) This is unfortunate because SO_REUSEADDR sockets have less requirements than non SO_REUSEADDR ones. If an application uses SO_REUSEADDR hint, it is to try to allow source ports being shared. So instead of picking a random port number in ip_local_port_range, lets try first in first half of the range. This gives more chances to use upper half of the range for the sockets with strong requirements (not using SO_REUSEADDR) Note this patch does not add a new sysctl, and only changes the way we try to pick port number. Signed-off-by: Eric Dumazet Cc: Marcelo Ricardo Leitner Cc: Flavio Leitner Acked-by: Flavio Leitner Signed-off-by: David S. Miller --- net/ipv4/inet_connection_sock.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c index b95fb26..60021d0 100644 --- a/net/ipv4/inet_connection_sock.c +++ b/net/ipv4/inet_connection_sock.c @@ -99,6 +99,7 @@ int inet_csk_get_port(struct sock *sk, unsigned short snum) struct net *net = sock_net(sk); int smallest_size = -1, smallest_rover; kuid_t uid = sock_i_uid(sk); + int attempt_half = (sk->sk_reuse == SK_CAN_REUSE) ? 1 : 0; local_bh_disable(); if (!snum) { @@ -106,6 +107,14 @@ int inet_csk_get_port(struct sock *sk, unsigned short snum) again: inet_get_local_port_range(net, &low, &high); + if (attempt_half) { + int half = low + ((high - low) >> 1); + + if (attempt_half == 1) + high = half; + else + low = half; + } remaining = (high - low) + 1; smallest_rover = rover = prandom_u32() % remaining + low; @@ -154,6 +163,11 @@ again: snum = smallest_rover; goto have_snum; } + if (attempt_half == 1) { + /* OK we now try the upper half of the range */ + attempt_half = 2; + goto again; + } goto fail; } /* OK, here is the one we will use. HEAD is -- 2.7.4