netdev - Re: virt-manager broken by bind(0) in net-next.

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Message-ID: <49841738.7050605@cosmosbay.com>
Date:	Sat, 31 Jan 2009 10:17:44 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Evgeniy Polyakov <zbr@...emap.net>
CC:	Stephen Hemminger <shemminger@...tta.com>,
	Herbert Xu <herbert@...dor.apana.org.au>, berrange@...hat.com,
	et-mgmt-tools@...hat.com, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: virt-manager broken by bind(0) in net-next.

Evgeniy Polyakov a écrit :
> On Fri, Jan 30, 2009 at 06:52:24PM -0800, Stephen Hemminger (shemminger@...tta.com) wrote:
>> My working hypothesis is:
>>   1. Something about Evgeniy's patch makes IPV6 (actually IPV4 in IPV6) be
>>      preferred over plain IPV4.
>>   2. Vino server (VNC) doesn't think ::ffff::127.0.0.1 is really the localhost
>>   3. protocol gets screwed up after that.
>>
>> It is probably reproducible with other services that support IPV6.
> 
> getaddrinfo() returns list of addresses and IPv6 was the first one iirc.
> Previously it bailed out, but with my change it will try again without
> reason for doing this. With the patch I sent based on Eric's observation
> things should be fine.
> 

Problem is your patch is wrong Evgeniy, please think about it litle bit more
and resubmit it. 

Take the time to run this $0.02 program, before and after your upcoming fix :


$ cat size.c
#include <net/inet_hashtables.h>
extern int printf(const char *, ...);
int main(int argc, char *argv[])
{
        printf("offsetof(struct inet_hashinfo, bsockets)=0x%x\n",
                offsetof(struct inet_hashinfo, bsockets));
        return 0;
}
$ make size.o ; gcc -o size size.o ; ./size
  CHK     include/linux/version.h
  CHK     include/linux/utsrelease.h
  SYMLINK include/asm -> include/asm-x86
  CALL    scripts/checksyscalls.sh
  CC      size.o
offsetof(struct inet_hashinfo, bsockets)=0x18


offset of bsockets being 0x18 or 0x20 is same result : bad because in
same cache line than ehash, ehash_locks, ehash_size, ehash_locks_mask,
bhash, bhash_size, unless your cpu is a Pentium.

Also, I suggest you change bsockets to something more appropriate, eg a
percpu counter.

Thank you.
Eric

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