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    Subject[PATCH] msi: Immediately mask and unmask msi-x irqs.
    Date

    This is a simplified and actually more comprehensive form of a bug
    fix from Mitch Williams <mitch.a.williams@intel.com>.

    When we mask or unmask a msi-x irqs the writes may be posted because
    we are writing to memory mapped region. This means the mask and
    unmask don't happen immediately but at some unspecified time in the
    future. Which is out of sync with how the mask/unmask logic work
    for ioapic irqs.

    The practical result is that we get very subtle and hard to track down
    irq migration bugs.

    This patch performs a read flush after writes to the MSI-X table for mask
    and unmask operations. Since the SMP affinity is set while the interrupt
    is masked, and since it's unmasked immediately after, no additional flushes
    are required in the various affinity setting routines.

    The testing by Mitch Williams on his especially problematic system should
    still be valid as I have only simplified the code, not changed the
    functionality.

    We currently have 7 drivers: cciss, mthca, cxgb3, forceth, s2io,
    pcie/portdrv_core, and qla2xxx in 2.6.21 that are affected by this
    problem when the hardware they driver is plugged into the right slot.

    Given the difficulty of reproducing this bug and tracing it down to
    anything that even remotely resembles a cause, even if people are
    being affected we aren't likely to see many meaningful bug reports, and
    the people who see this bug aren't likely to be able to reproduce this
    bug in a timely fashion. So it is best to get this problem fixed
    as soon as we can so people don't have problems.

    Then if people do have a kernel message stating "No irq for vector" we
    will know it is yet another novel cause that needs a complete new
    investigation.

    So here is a one liner that will hopefully be a part of 2.6.21.

    Cc: Mitch Williams <mitch.a.williams@intel.com>
    Cc: Greg KH <greg@kroah.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    ---
    drivers/pci/msi.c | 1 +
    1 files changed, 1 insertions(+), 0 deletions(-)

    diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
    index ad33e01..435c195 100644
    --- a/drivers/pci/msi.c
    +++ b/drivers/pci/msi.c
    @@ -94,6 +94,7 @@ static void msi_set_mask_bit(unsigned int irq, int flag)
    int offset = entry->msi_attrib.entry_nr * PCI_MSIX_ENTRY_SIZE +
    PCI_MSIX_ENTRY_VECTOR_CTRL_OFFSET;
    writel(flag, entry->mask_base + offset);
    + readl(entry->mask_base + offset);
    break;
    }
    default:
    --
    1.5.0.4
    -
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