netdev - Re: [PATCH] can-raw: Fix skb_orphan

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Date:	Sun, 01 Aug 2010 12:50:16 +0200
From:	Oliver Hartkopp <socketcan@...tkopp.net>
To:	David Miller <davem@...emloft.net>
CC:	eric.dumazet@...il.com, patrick.ohly@...el.com,
	netdev@...r.kernel.org, socketcan-core@...ts.berlios.de,
	matthias.fuchs@....eu
Subject: Re: [PATCH] can-raw: Fix skb_orphan_try handling

On 01.08.2010 10:03, David Miller wrote:
> From: Oliver Hartkopp <socketcan@...tkopp.net>
> Date: Fri, 30 Jul 2010 11:44:27 +0200
> 
>> Hello Eric, hello Patrick,
>>
>> Commit fc6055a5ba31e2c14e36e8939f9bf2b6d586a7f5 (net: Introduce
>> skb_orphan_try()) allows an early orphan of the skb and takes care on
>> tx timestamping, which needs the sk-reference in the skb on driver level.
>> So does the can-raw socket, which has not been taken into account here.
>>
>> The patch below adds a 'prevent_sk_orphan' bit in the skb tx shared info,
>> which fixes the problem discovered by Matthias Fuchs here:
>>
>>       http://marc.info/?t=128030411900003&r=1&w=2
> 
> Your patch sets this new value, but I never see it getting tested anywhere.
> 
> How does this work?


The flags are tested all together in skb_orphan_try() ...

See at

http://git.kernel.org/?p=linux/kernel/git/davem/net-next-2.6.git;a=commitdiff;h=fc6055a5ba31e2c14e36e8939f9bf2b6d586a7f5

+/*
+ * Try to orphan skb early, right before transmission by the device.
+ * We cannot orphan skb if tx timestamp is requested, since
+ * drivers need to call skb_tstamp_tx() to send the timestamp.
+ */
+static inline void skb_orphan_try(struct sk_buff *skb)
+{
+       if (!skb_tx(skb)->flags)
+               skb_orphan(skb);
+}

So my patch just added a new bit that's tested here but does not touch the
rest of the tx timestamp bits that are checked at this place.

Regards,
Oliver
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