On Fri, 2014-03-21 at 14:52 -0400, David Miller wrote:
> From: Eric Dumazet <eric.duma...@gmail.com>
> Date: Fri, 21 Mar 2014 05:50:50 -0700
>
> > It looks like a barrier() would be more appropriate.
>
> barrier() == __asm__ __volatile__(:::"memory")
Indeed, but now you mention it, ip_fast_csum() do not uses volatile
keyword on x86_64, and has no "m" constraint either.
This means that for the following hypothetical networking code :
void foobar(struct iphdr *iph, __be16 newlen, __be16 newid)
{
iph->tot_len = newlen;
iph->check = 0;
iph->check = ip_fast_csum((u8 *)iph, 5);
pr_err("%p\n", iph);
iph->id = newid;
iph->check = 0;
iph->check = ip_fast_csum((u8 *)iph, 5);
}
ip_fast_csum() is done _once_ only.
Following patch seems needed. Thats one another call for x86 code factorization
...
diff --git a/arch/x86/include/asm/checksum_64.h
b/arch/x86/include/asm/checksum_64.h
index e6fd8a026c7b..c67778544880 100644
--- a/arch/x86/include/asm/checksum_64.h
+++ b/arch/x86/include/asm/checksum_64.h
@@ -46,7 +46,7 @@ static inline __sum16 ip_fast_csum(const void *iph, unsigned
int ihl)
{
unsigned int sum;
- asm(" movl (%1), %0\n"
+ asm volatile(" movl (%1), %0\n"
" subl $4, %2\n"
" jbe 2f\n"
" addl 4(%1), %0\n"
--
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