[PATCH 2/2] nvme pci: try to allocate multiple irq vectors again in case of -EINVAL

[ming.lei@redhat.com (Ming Lei)]

On Thu, Dec 27, 2018@02:08:34PM +0100, Christoph Hellwig wrote:
> On Thu, Dec 27, 2018@04:21:38PM +0800, Ming Lei wrote:
> > On Wed, Dec 26, 2018@07:20:27PM +0100, Christoph Hellwig wrote:
> > > On Wed, Dec 26, 2018@06:37:55PM +0800, Ming Lei wrote:
> > > > It is observed on QEMU that pci_alloc_irq_vectors_affinity() may
> > > > returns -EINVAL when the requested number is too big(such as 64).
> > > 
> > > Which is not how this API is supposed to work and documented to work.
> > > 
> > > We need to fix pci_alloc_irq_vectors_affinity to not return a spurious
> > > error and just return the allocated number of vectors instead of
> > > hacking around that in drivers.
> > 
> > Yeah, you are right.
> > 
> > The issue is that QEMU nvme-pci is MSIX-capable only, and hasn't MSI
> > capability.
> > 
> > __pci_enable_msix_range() actually returns -ENOSPC, but __pci_enable_msi_range()
> > returns -EINVAL because dev->msi_cap is zero.
> > 
> > Maybe we need the following fix?
> 
> Should it matter?  We still get a negative vecs back, and still fall
> back to the next option.  Unless ther are no irqs available at all
> for the selected types pci_alloc_irq_vectors_affinity should never
> return an error.

The patch in last email does fix this issue.

In this case, the number of NVMe PCI's MSI-X table entries is 64, so
__pci_enable_msix_range() return -ENOSPC when we ask for 65.

However, the following __pci_enable_msi_range() returns -EINVAL because
the NVMe PCI isn't capable of MSI, then this error is returned from
pci_alloc_irq_vectors_affinity() finally to NVMe driver.

Of course, -EINVAL makes a difference because the current code only
tries to assign one irq vector in this case, and it shouldn't be
returned from pci_alloc_irq_vectors_affinity(), given there is enough
msix entries for fallback, right?

Thanks,
Ming