netdev - Re: [PATCH net-next v3] tuntap: Fix for a race in accessing numqueues

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Message-Id: <20140122.213316.1975984315340872670.davem@davemloft.net>
Date:	Wed, 22 Jan 2014 21:33:16 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	dominic.curran@...rix.com
Cc:	netdev@...r.kernel.org, jasowang@...hat.com, maxk@....qualcomm.com
Subject: Re: [PATCH net-next v3] tuntap: Fix for a race in accessing
 numqueues

From: Dominic Curran <dominic.curran@...rix.com>
Date: Wed, 22 Jan 2014 03:03:23 +0000

> A patch for fixing a race between queue selection and changing queues
> was introduced in commit 92bb73ea2("tuntap: fix a possible race between
> queue selection and changing queues").
> 
> The fix was to prevent the driver from re-reading the tun->numqueues
> more than once within tun_select_queue() using ACCESS_ONCE().
> 
> We have been experiancing 'Divide-by-zero' errors in tun_net_xmit() 
> since we moved from 3.6 to 3.10, and believe that they come from a 
> simular source where the value of tun->numqueues changes to zero 
> between the first and a subsequent read of tun->numqueues.
> 
> The fix is a simular use of ACCESS_ONCE(), as well as a multiply
> instead of a divide in the if statement.
> 
> Signed-off-by: Dominic Curran <dominic.curran@...rix.com>

Applied, thank you.
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