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tcp: Combat per-cpu skew in orphan tests.

Browse source 
As reported by Anton Blanchard when we use
percpu_counter_read_positive() to make our orphan socket limit checks,
the check can be off by up to num_cpus_online() * batch (which is 32
by default) which on a 128 cpu machine can be as large as the default
orphan limit itself.

Fix this by doing the full expensive sum check if the optimized check
triggers.

Reported-by: Anton Blanchard <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Acked-by: Eric Dumazet <[email protected]>
This commit is contained in:
David S. Miller 2010-08-25 02:27:49 -07:00
commit ad1af0fedb
3 changed files with 19 additions and 12 deletions
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5
net/ipv4/tcp.c
View file

@ -2011,11 +2011,8 @@ adjudge_to_death:
}
}
if (sk->sk_state != TCP_CLOSE) {
int orphan_count = percpu_counter_read_positive(
sk->sk_prot->orphan_count);
sk_mem_reclaim(sk);
if (tcp_too_many_orphans(sk, orphan_count)) {
if (tcp_too_many_orphans(sk, 0)) {
if (net_ratelimit())
printk(KERN_INFO "TCP: too many of orphaned "
"sockets\n");

8
net/ipv4/tcp_timer.c
View file

@ -66,18 +66,18 @@ static void tcp_write_err(struct sock *sk)
static int tcp_out_of_resources(struct sock *sk, int do_reset)
{
struct tcp_sock *tp = tcp_sk(sk);
int orphans = percpu_counter_read_positive(&tcp_orphan_count);
int shift = 0;
/* If peer does not open window for long time, or did not transmit
* anything for long time, penalize it. */
if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
orphans <<= 1;
shift++;
/* If some dubious ICMP arrived, penalize even more. */
if (sk->sk_err_soft)
orphans <<= 1;
shift++;
if (tcp_too_many_orphans(sk, orphans)) {
if (tcp_too_many_orphans(sk, shift)) {
if (net_ratelimit())
printk(KERN_INFO "Out of socket memory\n");