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Date: Sun, 22 Jun 2014 00:13:55 -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 Subject: Re: [PATCH net] xen-netback: bookkeep number of queues in our own module From: Wei Liu <wei.liu2@...rix.com> Date: Wed, 18 Jun 2014 15:09:18 +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. The usage of real_num_tx_queues in core driver is to cap queue > index to a valid value. In start_xmit we've already guarded against out > of range queue index so we should be fine. > > This fixes a regression introduced by multiqueue patchset in 3.16-rc1. > > Reported-by: Boris Ostrovsky <boris.ostrovsky@...cle.com> > Signed-off-by: Wei Liu <wei.liu2@...rix.com> I say you should have a select queue method at all. You're essentially providing a half-assed version of __netdev_pick_tx() except that: 1) You're _completely_ ignoring the socket hash, if any. 2) You're not allowing XPS to work, _at all_. I think you need to serious reevaluate providing any select queue method at all, just let netdev_pick_tx() do all the work. If you have some issue maintaining the release of queue resources, maintain that privately and keep those details in the queue resource allocation and freeing code _only_. Don't make it an issue that interferes at all with the normal mechanisms for SKB tx queue selection. Thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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