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

From: Jonathan Toppins <[email-masked]>
Date: Wed, 22 Oct 2014 19:38:31 -0400

On 10/22/14, 2:55 PM, Crestez Dan Leonard wrote:
> sg_init_one does virt_addr on the pointer which assumes it is directly accessible. But the tcp_md5sig_pool pointer comes from alloc_percpu which can return memory from the vmalloc area after the pcpu_first_chunk is exhausted. This looks wrong to me. I'm am getting crashes on mips and I believe this to be the cause.

Thinking about this more if the issue really is sg_init_one assumes a
directly accessible memory region, can we just modify the zone
allocation to GFP_DMA using alloc_percpu_gfp()? Does this satisfy the
assumptions made by sg_init_one?

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 1bec4e7..6924320 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2889,7 +2889,7 @@ static void __tcp_alloc_md5sig_pool(void)
        int cpu;
        struct tcp_md5sig_pool __percpu *pool;

-       pool = alloc_percpu(struct tcp_md5sig_pool);
+       pool = alloc_percpu_gfp(struct tcp_md5sig_pool, GFP_DMA);
        if (!pool)
                return;