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

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Message-ID: <20150713081040.GB8971@gondor.apana.org.au>
Date:	Mon, 13 Jul 2015 16:10:40 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
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, Jul 13, 2015 at 10:05:42AM +0200, Eric Dumazet wrote:
>
> 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)

I think UDP should be OK because the main creator of shared skbs
is af_packet and in that cast the IP stack will clone the skb upon
entry.  AFAIK there aren't any entities doing the shared skb trick
within the IP stack.

IOW the UDP stack does not have to worry about share skbs, unlike
netlink.

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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