linux-kernel - Re: [Bugfix] x86/PCI: Release PCI IRQ resource only if PCI device is disabled when unbinding

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Message-ID: <2835680.pSPaYk3eSL@vostro.rjw.lan>
Date:	Thu, 19 Mar 2015 12:29:06 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Thomas Hellstrom <thellstrom@...are.com>,
	"bp @ alien8 . de" <bp@...en8.de>, Lv Zheng <lv.zheng@...el.com>,
	"yinghai @ kernel . org" <yinghai@...nel.org>,
	"lenb @ kernel . org" <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [Bugfix] x86/PCI: Release PCI IRQ resource only if PCI device is disabled when unbinding

On Thursday, March 19, 2015 03:49:33 PM Jiang Liu wrote:
> On 2015/3/19 6:11, Bjorn Helgaas wrote:
> > On Tue, Mar 17, 2015 at 03:37:12PM +0800, Jiang Liu wrote:
> >> To support IOAPIC hot-removal, we need to release PCI interrupt resource
> >> when unbinding PCI device driver. But due to historical reason,
> >> /*
> >>  * We would love to complain here if pci_dev->is_enabled is set, that
> >>  * the driver should have called pci_disable_device(), but the
> >>  * unfortunate fact is there are too many odd BIOS and bridge setups
> >>  * that don't like drivers doing that all of the time.
> >>  * Oh well, we can dream of sane hardware when we sleep, no matter how
> >>  * horrible the crap we have to deal with is when we are awake...
> >>  */
> > 
> > Quoting the comment here (especially the last two lines) is overkill and
> > obscures the real point.  The important thing is that some drivers have
> > legitimate reasons for not calling pci_disable_device().
> Hi Bjorn,
> 	Thanks for review. I will rewrite the commit message.
> >> some drivers don't call pci_disable_device() when unloading, which
> >> prevents us from reallocating PCI interrupt resource on reloading
> >> PCI driver and causes regressions.
> > 
> > This isn't very clear.  I can believe that "drivers not calling
> > pci_disable_device()" means we don't release IRQ resources, which might
> > prevent you from hot-removing an IOAPIC.
> > 
> > But "drivers not calling pci_disable_device()" doesn't cause regressions.
> > 
> >> So release PCI interrupt resource only if PCI device is disabled when
> >> unbinding. By this way, we could support IOAPIC hot-removal on latest
> >> platforms and avoid regressions on old platforms.
> > 
> > Does this mean you can only hot-remove IOAPICs if all drivers for devices
> > using the IOAPIC call pci_disable_device()?  If so, it seems sort of
> > dubious that we have to rely on drivers for that.
> This is a quickfix for v4.0 merging window. We will try to solve this
> issue for next merging window.

If that is the plan, then I'd rather revert the offending commit and try
again in the next cycle.

Bjorn, what do you think?


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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