netdev - Re: [PATCH net-next 2/4] net: af_unix: implement stream sendpage support

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Message-Id: <1432165669.742118.274281209.1779FF2D@webmail.messagingengine.com>
Date:	Thu, 21 May 2015 01:47:49 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/4] net: af_unix: implement stream sendpage support

On Thu, May 21, 2015, at 01:21, Eric Dumazet wrote:
> On Wed, 2015-05-20 at 17:35 +0200, Hannes Frederic Sowa wrote:
> > This patch implements sendpage support for AF_UNIX SOCK_STREAM
> > +
> > +	if (newskb)
> > +		skb_queue_tail(&other->sk_receive_queue, newskb);
> 
> Are you sure we need the skb_queue_tail() here (taking spinlock) ?
> 
> This would tell us there might be a possible race.
> 
> A comment would be nice eventually.

Hmm, at first sight, I think we can change this to __skb_queue_tail.
sendpage does take state_lock and readlock mutex and thus blocks out
both, recvmsg and sendmsg. unix_stream_connect is also serialized by
state_lock.

I guess I used it because of unix_stream_sendmsg, where it is actually
necessary, as recvmsg does unlink skb without state_lock and sendmsg
doesn't hold reader mutex.

Thanks for the hint!

Bye,
Hannes
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