Re: [RFC PATCH] PCI: Disable MSI/MSI-X only if device is shutdown

Bandan Das
2015-03-13T03:10:00Z

Ccing Alex, he can probably confirm if my understanding is indeed correct.

Fam Zheng <famz@redhat.com> writes:

> On Thu, 03/12 19:56, Bandan Das wrote:
>> Hi Fam,
>>
>> Fam Zheng <famz@redhat.com> writes:
>>
>> > If the device doesn't support shutdown, disabling interrupts may cause
>> > trouble. For example, virtio-scsi-pci doesn't implement shutdown, and
>> > after we disable MSI-X, futher notifications from device will be
>> > delivered to IRQ, which is unexpected. This IRQ will not be cleared, and
>> > may prevent us from making progress, by keep triggering interrupts.
>> >
>> > Signed-off-by: Fam Zheng <famz@redhat.com>
>> > ---
>> > drivers/pci/pci-driver.c | 7 ++++---
>> > 1 file changed, 4 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
>> > index 3cb2210..fb29c96 100644
>> > --- a/drivers/pci/pci-driver.c
>> > +++ b/drivers/pci/pci-driver.c
>> > @@ -448,10 +448,11 @@ static void pci_device_shutdown(struct device *dev)
>> >
>> > pm_runtime_resume(dev);
>> >
>> > - if (drv && drv->shutdown)
>> > + if (drv && drv->shutdown) {
>> > drv->shutdown(pci_dev);
>> > - pci_msi_shutdown(pci_dev);
>> > - pci_msix_shutdown(pci_dev);
>> > + pci_msi_shutdown(pci_dev);
>> > + pci_msix_shutdown(pci_dev);
>> > + }
>>
>> If the driver doesn't provide a shutdown method and doesn't itself
>> disable MSI/MSI-X, then pci_msi(x)_shutdown won't be called anymore,
>> no ?
>
> Right.
>
>>
>> This is probably ok (but unclean) for a system shutdown, but could
>> cause problems for something like kexec ?
>
> Doesn't the reset in kexec clean this up during initialization?

I guess it would take the same path as a reboot.

> Without shutdown, anything in the driver is unclean anyway, for example
> free_irq is not called.

True, And that is why the MSI/-X shutdown functions are called here
because pci can't always rely on the individual device drivers to do
the right thing, but atleast can make a best effort at cleaning up.

> Fam