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    SubjectRe: [PATCH 2.6.21-rc5] MSI: read-flush MSI-X table
    On Mon, Mar 26, 2007 at 04:18:22PM -0700, Mitch Williams wrote:
    > This patch fixes a kernel bug which is triggered when using the
    > irqbalance daemon with MSI-X hardware.
    >
    > Because both MSI-X interrupt messages and MSI-X table writes are posted,
    > it's possible for them to cross while in-flight. This results in
    > interrupts being received long after the kernel thinks they're disabled,
    > and in interrupts being sent to stale vectors after rebalancing.
    >
    > This patch performs a read flush after writes to the MSI-X table for
    > enable/disable and rebalancing operations.

    Why wouldn't MSI have the same problems as MSI-X?

    ...
    > diff -urpN -X dontdiff linux-2.6.21-rc4-clean/drivers/pci/msi.c linux-2.6.21-rc4/drivers/pci/msi.c
    > --- linux-2.6.21-rc4-clean/drivers/pci/msi.c 2007-03-19 16:16:32.000000000 -0700
    > +++ linux-2.6.21-rc4/drivers/pci/msi.c 2007-03-21 12:44:51.000000000 -0700
    > @@ -68,6 +68,29 @@ static void msix_set_enable(struct pci_d
    > }
    > }
    >
    > +void msix_flush_writes(unsigned int irq)
    > +{
    > + struct msi_desc *entry;
    > +
    > + entry = get_irq_msi(irq);
    > + BUG_ON(!entry || !entry->dev);
    > + switch (entry->msi_attrib.type) {
    > + case PCI_CAP_ID_MSI:
    > + /* nothing to do */
    > + break;
    > + case PCI_CAP_ID_MSIX:
    > + {
    > + int offset = entry->msi_attrib.entry_nr * PCI_MSIX_ENTRY_SIZE +
    > + PCI_MSIX_ENTRY_VECTOR_CTRL_OFFSET;
    > + readl(entry->mask_base + offset);
    > + break;
    > + }
    > + default:
    > + BUG();
    > + break;
    > + }
    > +}

    PCI_CAP_ID_MSI case seems wrong to me.
    I was expecting a readl() in that case as well.

    thanks,
    grant
    -
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