Subject: Re: [RFC] tcp md5 use of alloc_percpu

From: David Ahern <[email-masked]>
Date: Wed, 22 Oct 2014 22:40:36 -0600

On 10/22/14, 12:55 PM, Crestez Dan Leonard wrote:
> Hello,
>
> It seems that the TCP MD5 feature allocates a percpu struct tcp_md5sig_pool and uses part of that memory for a scratch buffer to do crypto on. Here is the relevant code:

This is a forward port of a local change to address the problem (local 
kernel version is 3.4 so perhaps my quick bump to top of tree is off but 
it shows the general idea). Been on my to-do list to figure out why this 
is needed, but it seems related to your problem:

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 1bec4e76d88c..833a676bd4b0 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2941,7 +2941,7 @@ struct tcp_md5sig_pool *tcp_get_md5sig_pool(void)
     local_bh_disable();
     p = ACCESS_ONCE(tcp_md5sig_pool);
     if (p)
-       return raw_cpu_ptr(p);
+       return __va(per_cpu_ptr_to_phys(raw_cpu_ptr(p)));

     local_bh_enable();
     return NULL;

David