Re: [PATCH] net: Allocate RX and TX queues in alloc_netdev_mq

[David Miller <davem@davemloft.net>]

From: Tom Herbert <therbert@google.com>
Date: Thu, 28 Oct 2010 10:45:45 -0700 (PDT)

> Both TX and RX queue allocations in the netdev structure had been moved
> to register_device with the idea that the number of queues could be
> changed between device allocation and registration.  It was determined
> that changing the num_queues after the call to alloc_netdev_mq was not
> a good idea, so that was abandoned.  Also, some drivers call
> netif_queue_start without registering device, which causes panic
> when dev->_tx queue structure is accessed.  This patch moves queue
> allocations back to alloc_netdev_mq to fix these issues.
> 
> Signed-off-by: Tom Herbert <therbert@google.com>

Changing the TX queue state with a netif_stop_queue() call or
similar was always completely pointless and frankly a bug.

So that should not influence the motivation behind this change
at all.

In fact I _like_ that it crashes now so that we are forced
to fix these cases.

Really, the queue state is absolutely immaterial during
device allocation and registration.  It's state is
%100 "don't care" until ->open() is invoked.

So any code that touches the queue state at these earlier points in
time is completely extraneous if not broken.