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

[David Miller <davem@xxxxxxxxxxxxx>]

From: Wei Liu <wei.liu2@xxxxxxxxxx>
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@xxxxxxxxxx>
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>

Applied, thank you.

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