netdev - Re: [PATCHv2 net] sunvnet: set queue mapping when doing packet copies

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Date:	Thu, 29 Jan 2015 14:19:42 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David L Stevens <david.stevens@...cle.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Sowmini Varadhan <sowmini.varadhan@...cle.com>
Subject: Re: [PATCHv2 net] sunvnet: set queue mapping when doing packet
 copies

On Thu, 2015-01-29 at 16:36 -0500, David L Stevens wrote:

> In general the destructor should match the allocator, right? So it bothers me
> here that we'd be replacing it in an skb allocated with alloc_and_align_skb(),
> with an an arbitrary destructor from an skb NOT allocated with alloc_and_align_skb().
> If it has a different destructor that does special handling related to the allocator,
> it is the original skb, not the new one, that needs the old destructor. This TCP
> accounting has less to do with the buffer destructor than with the freeing of the
> contents of the buffer, but that isn't necessarily true for all destructors.
> 
> Checking for a known, specific destructor is less troubling, so I don't want
> to remove the test entirely.
> 
> Since the concern here is specifically TCP flow control, do you think it's sufficient
> to substitute tcp_wfree for the sock_wfree here?

The concern is also for UDP.

Right now a single UDP flow can flood your network, even if application
or admin cared to set a low SO_SNDBUF.

I guess you can extend the test to sock_wfree and tcp_wfree, but :

You have to EXPORT_SYMBOL(tcp_wfree)

Add an #ifdef CONFIG_INET   (take a look at skb_orphan_partial())

Thanks







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