linux-kernel - Re: [PATCH][tentative] PCI / ACPI: Rework PCI host bridge removal to avoid sysfs warnings

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Date:	Fri, 03 Jan 2014 01:45:28 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH][tentative] PCI / ACPI: Rework PCI host bridge removal to avoid sysfs warnings

On Thursday, January 02, 2014 02:47:04 PM Yinghai Lu wrote:
> On Tue, Dec 31, 2013 at 1:03 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > On Tuesday, December 31, 2013 10:45:46 AM Yinghai Lu wrote:
> >> On Mon, Dec 30, 2013 at 5:15 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >> > On Monday, December 30, 2013 01:51:28 PM Rafael J. Wysocki wrote:
> >> >> > We have patches that need to stop ioapic and iommu between
> >> >> > pci_stop_root_bus and pci_remove_root_bus.
> >> >
> >> > BTW, what *exactly* do they need to be stopped between?  After these two patches:
> >>
> >> need to stop regular pci drivers before stop "driver" for ioapic/dmar.
> >>
> >> >
> >> >> > Please check if the problem still happen after
> >> >> >
> >> >> > http://git.kernel.org/cgit/linux/kernel/git/helgaas/pci.git/patch/?id=c4a0a5d964e90b93eb4101c3927b788e083e530f
> >> >> >
> >> >> > http://git.kernel.org/cgit/linux/kernel/git/helgaas/pci.git/patch/?id=e3b439e1d315aff59c1b4f0fc43c5cd2d82b4138
> >> >
> >> > pci_stop_root_bus() is just a walk over devices on the root bus stopping
> >> > them and pci_remove_root_bus() starts with the removal of those devices.
> >> >
> >> > Surely, those two list walks can be combined into one?
> >>
> >> maybe ok, but we have to problem to make sure stop pci drivers before
> >> "driver" for ioapic/dmar.
> >
> > That's fine, but ioapic/dmar stopping need not happen between the stopping of
> > drivers and removing of devices on the root bus I suppose?
> >
> > Actually, I think that the ioapic/dmar stopping should be carried out after
> > removing all of the root bus devices, or it can be racy with respect to a
> > driver reload.  Isn't that the case?
> 
> No. It should be before removing all root bus devices.
> as they need to access the pci devices during stop ioapic and dmar.
> 
> Also ioapic itself could one one pci device.

Well, if we stop drivers first, then stop ioapic/dmar and *then* remove
devices, it is possible to rebind a driver to a device after ioapic/dmar has
been stopped, which I guess will not lead to anything nice?

Rafael

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