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

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Date:	Thu, 09 Jan 2014 01:10:26 +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 Wednesday, January 08, 2014 03:41:52 PM Yinghai Lu wrote:
> On Mon, Jan 6, 2014 at 12:41 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> 
> >> Not sure how that could happen.
> >>
> >> If it would really happen, we could set dev->match_driver to 0 in pci_stop_dev.
> >
> > Simply, run "modprobe -r driver && modprobe driver" in a loop and
> > remove the PCI host bridge the given device is on in parallel to that.  Chances
> > are, you'll see some nice breakage.
> 
> I would suggest using match_driver prevent driver from attaching again.

Yes, we can do that.  Some locking is needed for it to be non-racy, however.

Anyway, we still have the problem with race conditions between different PCI
removal/rescan code paths.  And I'm still going to prepare a patch to use
the remove-rescan mutex to address those race conditions and that patch should
help here too.

> 
> ---
>  drivers/pci/remove.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> Index: linux-2.6/drivers/pci/remove.c
> ===================================================================
> --- linux-2.6.orig/drivers/pci/remove.c
> +++ linux-2.6/drivers/pci/remove.c
> @@ -11,6 +11,7 @@ static void pci_stop_dev(struct pci_dev
>          pci_proc_detach_device(dev);
>          pci_remove_sysfs_dev_files(dev);
>          device_release_driver(&dev->dev);
> +        dev->match_driver = false;
>          dev->is_added = 0;
>      }
> 
> 
> >
> > Also what happens if somebody uses the "remove" sysfs attribute on a device
> > needed by ioapic/dmar?
> 
> Good question, we will have problem in that case.
> To make it simple, we may hide the "remove" in sysfs for ioapic pci device ?

Yeah, we need to do that if using that attribute may lead to problems.

Thanks,
Rafael

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