netdev - Re: [PATCH] netlink: enable skb header refcounting before sending first broadcast

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Message-ID: <1436774742.9402.3.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 13 Jul 2015 10:05:42 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH] netlink: enable skb header refcounting before sending
 first broadcast

On Mon, 2015-07-13 at 15:23 +0800, Herbert Xu wrote:

> The real issue here is that the recv path no longer handles shared
> skbs.  So either we need to fix the recv path to not touch skbs
> without cloning them, or we need to get rid of the use of shared
> skbs in netlink.
> 
> In fact it looks I introduced the bug way back in
> 
> commit a59322be07c964e916d15be3df473fb7ba20c41e
> Author: Herbert Xu <herbert@...dor.apana.org.au>
> Date:   Wed Dec 5 01:53:40 2007 -0800
> 
>     [UDP]: Only increment counter on first peek/recv
> 
> I will try to mend this error :)
> 
> Cheers,

Herbert, UDP peek support is very buggy anyway, because of deferred
checksums

__skb_checksum_complete() will happily manipulate csum, ip_summed,
csum_complete_sw & csum_valid

Ideally, peek should never touch skb (but skb->users)


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