netdev - Re: Regarding to your linux kernel CL

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Message-ID: <AANLkTinuis9vneb44W18jwLZ=KzFJQeVGg-FhGsWgK7-@mail.gmail.com>
Date:	Wed, 6 Oct 2010 01:04:18 -0700
From:	Chung-Yih Wang (王崇懿) 
	<cywang@...gle.com>
To:	Herbert Xu <herbert@...dor.hengli.com.au>
Cc:	Timo Teräs <timo.teras@....fi>,
	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: Regarding to your linux kernel CL

I have submitted a patch([PATCH] net: Fix sk_dst_check() to reset the
obsolete dst_entry of a socket) for this, please reply to that thread
then.

Thanks,
Chung-yih

On Wed, Oct 6, 2010 at 12:59 AM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
> On Wed, Oct 06, 2010 at 10:02:56AM +0300, Timo Teräs wrote:
>>
>> What's the problem here? sk_dst_check not honoring if dst->obsolete>0 ?
>> Sounds like the sk_dst_check was buggy in the first place.
>
> Well the problem is that before we changed ip4_dst_check, everything
> worked properly.  With IPv6, whenever a route is released, the serial
> number is always updated accordingly.  This means that ip6_dst_check
> will always return NULL when obsolete > 1.
>
> The old ip4_dst_check also satisfied this requirement since it always
> returns NULL.
>
>> Looks like there's still some code around that does not do what the
>> obsolete field has been used for a long time.
>>   obsolete =  0, dst entry is ok
>>   obsolete = -1, you need to call ops->check for this entry
>>   obsolete >  0, this entry is invalid
>>
>> So net/core/sock.c needs fixing. Just if we should change dst_check()
>> too, I'm not sure.
>>
>> Should we fix sk_dst_check to use dst_check(), and dst_check() to check
>> for dst->obsolete>0 ?
>
> Yes this should work too.  However, I was never totally happy with
> this new dst->obsolete logic which means that we're doing an
> indirect call for every single packet which almost always does
> nothing.
>
> Perhaps we should move the genid/cookie logic into the dst so that
> we can eliminate the dst->check call or at least make it a lot less
> frequent.
>
> Cheers,
> --
> Email: Herbert Xu <herbert@...dor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
>
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