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Re: [PATCHv6 2/7] pci: child bus alloc fix on constrained resource

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On Thu, Dec 17, 2015 at 11:27:18AM -0600, Bjorn Helgaas wrote:
> On Mon, Dec 07, 2015 at 02:32:24PM -0700, Keith Busch wrote:
> > +	if (busnr > parent->busn_res.end) {
> > +		dev_printk(KERN_DEBUG, &parent->dev,
> > +			  "can not alloc bus:%d under %pR\n", busnr,
> > +			  &parent->busn_res);
> > +		return NULL;
> 
> Can you take a look at 1820ffdccb9b ("PCI: Make sure bus number resources
> stay within their parents bounds") and 12d8706963f0 ("Revert "PCI: Make
> sure bus number resources stay within their parents bounds"")?
> 
> This is implemented differently, but it seems like it might expose the same
> problem we found with 1820ffdccb9b.
> 
> If you could take a look and confirm that "no, this does something
> differently than 1820ffdccb9b did" or "yes, this might expose that problem
> again," that would help.

Thank you for the references. I think 1820ffdccb9b had the check too
late, creating the child bus with resource conflicts. That'd probably
make it appear unavailable. But I believe this new proposal will still
break the same setup for a different reason.

We can live with this issue for now if we want to drop this patch from
the series. The only way we encounter a problem is when the config space
aperture is artificially constrained, so I can request the feature be
put on hold while a better fix is developed.
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Re: [PATCHv6 2/7] pci: child bus alloc fix on constrained resource Bjorn Helgaas <helgaas@kernel.org> - 2015-12-17 18:30 +0100
  Re: [PATCHv6 2/7] pci: child bus alloc fix on constrained resource Keith Busch <keith.busch@intel.com> - 2015-12-17 19:00 +0100

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