netdev - Re: [PATCH net v3] xen-netback: bookkeep number of active queues in our own module

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Date:	Wed, 25 Jun 2014 16:00:14 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	wei.liu2@...rix.com
Cc:	xen-devel@...ts.xen.org, netdev@...r.kernel.org,
	boris.ostrovsky@...cle.com, ian.campbell@...rix.com,
	paul.durrant@...rix.com
Subject: Re: [PATCH net v3] xen-netback: bookkeep number of active queues
 in our own module

From: Wei Liu <wei.liu2@...rix.com>
Date: Mon, 23 Jun 2014 10:50:17 +0100

> The original code uses netdev->real_num_tx_queues to bookkeep number of
> queues and invokes netif_set_real_num_tx_queues to set the number of
> queues. However, netif_set_real_num_tx_queues doesn't allow
> real_num_tx_queues to be smaller than 1, which means setting the number
> to 0 will not work and real_num_tx_queues is untouched.
> 
> This is bogus when xenvif_free is invoked before any number of queues is
> allocated. That function needs to iterate through all queues to free
> resources. Using the wrong number of queues results in NULL pointer
> dereference.
> 
> So we bookkeep the number of queues in xen-netback to solve this
> problem. This fixes a regression introduced by multiqueue patchset in
> 3.16-rc1.
> 
> There's another bug in original code that the real number of RX queues
> is never set. In current Xen multiqueue design, the number of TX queues
> and RX queues are in fact the same. We need to set the numbers of TX and
> RX queues to the same value.
> 
> Also remove xenvif_select_queue and leave queue selection to core
> driver, as suggested by David Miller.
> 
> Reported-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Signed-off-by: Wei Liu <wei.liu2@...rix.com>

Applied, thank you.
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