Re: Spurious "TCP: too many of orphaned sockets", unable to allocate sockets

[David Miller <davem@davemloft.net>]

From: Anton Blanchard <anton@samba.org>
Date: Wed, 25 Aug 2010 17:16:26 +1000

> We have a machine running a network test that regularly hits:
> 
> TCP: too many of orphaned sockets
> 
> Which comes from:
> 
>                 int orphan_count = percpu_counter_read_positive(
>                                                 sk->sk_prot->orphan_count);
> 
>                 sk_mem_reclaim(sk);
>                 if (tcp_too_many_orphans(sk, orphan_count)) {
...
> 2. Even with this fixed we could hit the original issue. We have been known to
> test on 1024 thread boxes and we would have the possibility of 32 * 1024
> = 32k slack in the percpu counters. On this box tcp_max_orphans will be
> 64k after the fix which is a bit close for comfort. Should we do anything here?

Solution seems simple, if the too many orphan check triggers, simply
redo the check using the expensive but more accurate per-cpu counter
read (which avoids the skew) to make sure.