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

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Message-ID: <jpg8uf1twxs.fsf@redhat.com>
Date:	Thu, 12 Mar 2015 23:09:51 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Fam Zheng <famz@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-pci@...r.kernel.org,
	Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [RFC PATCH] PCI: Disable MSI/MSI-X only if device is shutdown

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

Fam Zheng <famz@...hat.com> writes:

> On Thu, 03/12 19:56, Bandan Das wrote:
>> Hi Fam,
>> 
>> Fam Zheng <famz@...hat.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@...hat.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
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