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Date: Wed, 18 Jun 2014 15:21:53 +0100 From: Wei Liu <wei.liu2@...rix.com> To: Boris Ostrovsky <boris.ostrovsky@...cle.com> CC: Wei Liu <wei.liu2@...rix.com>, <xen-devel@...ts.xen.org>, <netdev@...r.kernel.org>, Ian Campbell <ian.campbell@...rix.com>, David Vrabel <david.vrabel@...rix.com> Subject: Re: [PATCH net] xen-netback: bookkeep number of queues in our own module On Wed, Jun 18, 2014 at 10:18:50AM -0400, Boris Ostrovsky wrote: > On 06/18/2014 10:09 AM, Wei Liu wrote: > >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. > > > David sent a couple of patches earlier today that I have been testing and > they appear to fix both netfront and netback. (I am waiting for 32-bit to > finish) > > http://lists.xenproject.org/archives/html/xen-devel/2014-06/msg02308.html > I saw that, but they don't fix this backend bug. Try crashing the guest before it connects to backend. As I said in commit message: > >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 netif_set_real_num_tx_queues will need to be removed anyway. Wei. -- 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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