netdev - Re: [PATCH 3/3] vhost-net: use lock_sock_fast() in peek_head

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Message-ID: <1300038092.2761.41.camel@edumazet-laptop>
Date:	Sun, 13 Mar 2011 18:41:32 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Jason Wang <jasowang@...hat.com>, virtualization@...ts.osdl.org,
	netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] vhost-net: use lock_sock_fast() in peek_head_len()

Le dimanche 13 mars 2011 à 18:43 +0200, Michael S. Tsirkin a écrit :
> On Sun, Mar 13, 2011 at 05:32:07PM +0100, Eric Dumazet wrote:
> > Le dimanche 13 mars 2011 à 18:19 +0200, Michael S. Tsirkin a écrit :
> > 
> > > Other side is in drivers/net/tun.c and net/packet/af_packet.c
> > > At least wrt tun it seems clear socket is not locked.
> > 
> > Yes (assuming you refer to tun_net_xmit())
> > 
> > > Besides queue, dequeue seems to be done without socket locked.
> > > 
> > 
> > It seems this code (assuming you speak of drivers/vhost/net.c ?) has
> > some races indeed.
> > 
> 
> Hmm. Any more besides the one fixed here?
> 

If writers and readers dont share a common lock, how can they reliably
synchronize states ?

For example, the check at line 420 seems unsafe or useless.

skb_queue_empty(&sock->sk->sk_receive_queue)



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