linux-kernel - Re: [PATCH] x86/PCI: Fully disable devices before releasing IRQ resource

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Date:	Thu, 05 Mar 2015 20:51:52 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	x86@...nel.org, rjw@...ysocki.net, mingo@...hat.com, bp@...en8.de,
	lv.zheng@...el.com, hpa@...or.com, tglx@...utronix.de,
	yinghai@...nel.org, lenb@...nel.org, linux-pci@...r.kernel.org,
	tony.luck@...el.com, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/PCI: Fully disable devices before releasing IRQ
 resource

On Fri, 2015-03-06 at 09:49 +0800, Jiang Liu wrote:
> On 2015/3/6 5:06, Alex Williamson wrote:
> > The IRQ resource for a device is established when pci_enabled_device()
> > is called on a fully disabled device (ie. enable_cnt == 0).  With
> > commit b4b55cda5874 ("x86/PCI: Refine the way to release PCI IRQ
> > resources") this same IRQ resource is released when the driver is
> > unbound from the device, regardless of the enable_cnt.  This presents
> > the situation that an ill-behaved driver can now make a device
> > unusable to subsequent drivers by an imbalance in their use of
> > pci_enable/disable_device().  It's one thing to break your own device
> > if you're one of these ill-behaved drivers, but it's a serious
> > regression for secondary drivers like vfio-pci, which are innocent
> > of the transgressions of the previous driver.
> > 
> > Resolve by pushing the device to a fully disabled state before
> > releasing the IRQ resource.
> > 
> > Fixes: b4b55cda5874 ("x86/PCI: Refine the way to release PCI IRQ resources")
> > Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> > Cc: Jiang Liu <jiang.liu@...ux.intel.com>
> > ---
> >  arch/x86/pci/common.c |   13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
> > index 3d2612b..4810194 100644
> > --- a/arch/x86/pci/common.c
> > +++ b/arch/x86/pci/common.c
> > @@ -527,8 +527,19 @@ static int pci_irq_notifier(struct notifier_block *nb, unsigned long action,
> >  	if (action != BUS_NOTIFY_UNBOUND_DRIVER)
> >  		return NOTIFY_DONE;
> >  
> > -	if (pcibios_disable_irq)
> > +	if (pcibios_disable_irq) {
> > +		/*
> > +		 * Broken drivers may allow a device to be .remove()'d while
> > +		 * still enabled.  pci_enable_device() will only re-establish
> > +		 * dev->irq if the devices is fully disabled.  So if we want
> > +		 * to release the IRQ, we need to make sure the next driver
> > +		 * can re-establish it using pci_enable_device().
> > +		 */
> > +		while (pci_is_enabled(dev))
> > +			pci_disable_device(dev);
> > +
> >  		pcibios_disable_irq(dev);
> > +	}
> Hi Alex,
> 	Thanks for debugging and fixing it.
> 	Will it be feasible to give a debug message to remind those
> driver authors to correctly disable PCI when unbinding?

I can certainly add a warning to the loop, it loses a bit of its teeth
here though since we can't specify which driver to blame at this point.
Maybe that warning and perhaps this enabling roll-back should happen in
drivers/pci/pci-driver.c:pci_device_remove().  Bjorn, would you prefer
it be done generically there?  Thanks,

Alex

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