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tcp: improve REUSEADDR/NOREUSEADDR cohabitation

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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 <edumazet@google.com>
Cc: Marcelo Ricardo Leitner <mleitner@redhat.com>
Cc: Flavio Leitner <fbl@redhat.com>
Acked-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2015-05-20 10:59:02 -07:00 committed by David S. Miller
parent f5af1f57a2
commit 946f9eb226
1 changed files with 14 additions and 0 deletions
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14
net/ipv4/inet_connection_sock.c
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@ -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