netdev - Re: [PATCH RFC] unix: account skb memory to receiving socket's sk_rmem

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Date:	Tue, 26 Mar 2013 08:53:38 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	netdev@...r.kernel.org, yannick@...hler.name,
	xiyou.wangcong@...il.com, davem@...emloft.net
Subject: Re: [PATCH RFC] unix: account skb memory to receiving socket's
 sk_rmem_alloc on sending

On Tue, 2013-03-26 at 01:17 +0100, Hannes Frederic Sowa wrote:

> This is the newest version of this patch. I only stripped out the setting
> of the SOCK_USE_WRITE_QUEUE socket flag (I was unsure if otherwise
> sock_wfree needed the socket lock but I am pretty confident that is
> is not needed). Perhaps someone finds some time to have a look at this
> patch. Also, if you come up with things my test case does not cover yet
> please let me know and I will catch up with the tests.
> 
> Patch is based on net-next.
> 
> Thanks!
> 
> [PATCH RFC] unix: account skb memory to receiving socket's sk_rmem_alloc on sending
> 
> In case of unix datagram sockets, skb memory was only accounted in the
> sending socket's sk_wmem_alloc. Hence, if one receiver would stop to
> receive frames on its socket, the sending socket's send buffer space
> could get exhausted and the socket would block sending datagrams to
> other destionations, too.
> 
> This patch places the refcounted peer's unix address for AF_UNIX
> SOCK_DGRAM sockets into the skb's UNIXCB. So a reference from the skb
> to the receiving struct sock can be set and so enables to do proper skb
> destructor handling for rmem and wmem. Buffer memory is then accounted
> to the receiving socket. If the socket rmem is exhausted the normal
> blocking and timeout behaviour kicks in.
> 
> Resource exhausion protection for unix dgram sockets is now based
> only on sockets rmem checking. Unix dgram sockets do not rely on
> sk_max_ack_backlog anymore. The controls for this are
> /proc/sys/net/core/{r,w}mem_{default,max}.
> 
> This patch also changes the reporting of unix dgram rqueue size, as it
> now reports not only the size of the first fragment but the amount of
> readable memory for the socket.
> 
> Based on the patches from Yannick Koehler and Cong Wang.

This opens the possibility of a sender to flood a receiver, instead of
being blocked by its own sndbuf.

Do we want such regression ? How many applications might rely on
existing behavior ?

Its not clear what is the appropriate way to handle this.



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