[PATCH] PCI/MSI: preference to returning -ENOSPC from pci_alloc_irq_vectors_affinity

[Ming Lei <ming.lei@redhat.com>]

The API of pci_alloc_irq_vectors_affinity() requires to return -ENOSPC
if fewer than @min_vecs interrupt vectors are available for @dev.

However, if a device supports MSI-X but not MSI and a caller requests
@min_vecs that can't be satisfied by MSI-X, we previously returned
-EINVAL (from the failed attempt to enable MSI), not -ENOSPC.

Users of pci_alloc_irq_vectors_affinity() may try to reduce irq vectors
and allocate vectors again in case that -ENOSPC is returned, such as NVMe,
so we need to respect the current interface and give preference to -ENOSPC.

Especially the min/max vecs doesn't work correctly when using the
irq_affinity nr_sets because rebalancing the set counts is driver specific.
To get around that, drivers using nr_sets have to set min and max to the same
value and handle the "reduce and try again".

Cc: Jens Axboe <axboe@fb.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: linux-nvme@lists.infradead.org
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/pci/msi.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 7a1c8a09efa5..4c0b47867258 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -1168,7 +1168,8 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
 				   const struct irq_affinity *affd)
 {
 	static const struct irq_affinity msi_default_affd;
-	int vecs = -ENOSPC;
+	int msix_vecs = -ENOSPC;
+	int msi_vecs = -ENOSPC;
 
 	if (flags & PCI_IRQ_AFFINITY) {
 		if (!affd)
@@ -1179,16 +1180,17 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
 	}
 
 	if (flags & PCI_IRQ_MSIX) {
-		vecs = __pci_enable_msix_range(dev, NULL, min_vecs, max_vecs,
-				affd);
-		if (vecs > 0)
-			return vecs;
+		msix_vecs = __pci_enable_msix_range(dev, NULL, min_vecs,
+						    max_vecs, affd);
+		if (msix_vecs > 0)
+			return msix_vecs;
 	}
 
 	if (flags & PCI_IRQ_MSI) {
-		vecs = __pci_enable_msi_range(dev, min_vecs, max_vecs, affd);
-		if (vecs > 0)
-			return vecs;
+		msi_vecs = __pci_enable_msi_range(dev, min_vecs, max_vecs,
+						  affd);
+		if (msi_vecs > 0)
+			return msi_vecs;
 	}
 
 	/* use legacy irq if allowed */
@@ -1199,7 +1201,9 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
 		}
 	}
 
-	return vecs;
+	if (msix_vecs == -ENOSPC)
+		return -ENOSPC;
+	return msi_vecs;
 }
 EXPORT_SYMBOL(pci_alloc_irq_vectors_affinity);
 
-- 
2.9.5