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    Subject[PATCH AUTOSEL 4.19 173/219] PCI/MSI: Return -ENOSPC from pci_alloc_irq_vectors_affinity()
    Date
    From: Ming Lei <ming.lei@redhat.com>

    [ Upstream commit 77f88abd4a6f73a1a68dbdc0e3f21575fd508fc3 ]

    The API of pci_alloc_irq_vectors_affinity() says it returns -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.

    When -ENOSPC is returned, callers may reduce the number IRQs they request
    and try again. Most callers can use the @min_vecs and @max_vecs
    parameters to avoid this retry loop, but that doesn't work when using IRQ
    affinity "nr_sets" because rebalancing the sets is driver-specific.

    This return value bug has been present since pci_alloc_irq_vectors() was
    added in v4.10 by aff171641d18 ("PCI: Provide sensible IRQ vector
    alloc/free routines"), but it wasn't an issue because @min_vecs/@max_vecs
    removed the need for callers to iteratively reduce the number of IRQs
    requested and retry the allocation, so they didn't need to distinguish
    -ENOSPC from -EINVAL.

    In v5.0, 6da4b3ab9a6e ("genirq/affinity: Add support for allocating
    interrupt sets") added IRQ sets to the interface, which reintroduced the
    need to check for -ENOSPC and possibly reduce the number of IRQs requested
    and retry the allocation.

    Signed-off-by: Ming Lei <ming.lei@redhat.com>
    [bhelgaas: changelog]
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    Cc: Jens Axboe <axboe@fb.com>
    Cc: Keith Busch <keith.busch@intel.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 af24ed50a2452..971dddf62374f 100644
    --- a/drivers/pci/msi.c
    +++ b/drivers/pci/msi.c
    @@ -1155,7 +1155,8 @@ 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)
    @@ -1166,16 +1167,17 @@ 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 */
    @@ -1186,7 +1188,9 @@ 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);

    --
    2.20.1
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