linux-kernel - Re: [PATCH] PCI / hotplug / ACPI: Check ignore

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Message-ID: <20150522214416.GJ32152@google.com>
Date:	Fri, 22 May 2015 16:44:16 -0500
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Linux PCI <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	lorenzo.stanco@...il.com, tiagdtd-lava@...oo.de
Subject: Re: [PATCH] PCI / hotplug / ACPI: Check ignore_hotplug for all
 downstream devices

[+cc Lorenzo, tiagdtd-lava]

On Wed, May 20, 2015 at 02:14:13AM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> If the ignore_hotplug flag is set for a PCI device without an ACPI
> companion and a bus check notification is received for an ancestor
> bridge that is not the device's parent, ACPIPHP will ignore that
> flag.
> 
> Namely, in that case acpiphp_check_bridge() is called for the target
> bridge and if all of the devices immediately below the bridge are
> still present, trim_stale_devices() will be called for each of them.
> That function recursively walks the hierarchy downwards and removes
> device objects corresponding to devices that don't appear to be
> present any more.  Unfortunately, it only checks ignore_hotplug
> for devices having ACPI companions, so it will remove the others
> (if they don't respond) regardless of the ignore_hotplug value.
> 
> Fix the problem by making trim_stale_devices() take ignore_hotplug
> into consideration regardless of whether or not an ACPI companion
> is present for the device it has been called for.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Applied to pci/hotplug for v4.2, thanks!

I cc'd Lorenzo and tiagdtd-lava in hopes they can test this patch and see
whether it resolves https://bugzilla.kernel.org/show_bug.cgi?id=61891 .

The branch with this patch applied is here:
https://git.kernel.org/cgit/linux/kernel/git/helgaas/pci.git/log/?h=pci/hotplug

> ---
> 
> This may fix BZ61891, but even if it doesn't, the bug is quite obvious to me.
> 
> Should be applicable since commit b440bde74f04 (PCI: Add pci_ignore_hotplug()
> to ignore hotplug events for a device) which shipped in 3.17.
> 
> ---
>  drivers/pci/hotplug/acpiphp_glue.c |    5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> Index: linux-pm/drivers/pci/hotplug/acpiphp_glue.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/hotplug/acpiphp_glue.c
> +++ linux-pm/drivers/pci/hotplug/acpiphp_glue.c
> @@ -632,15 +632,14 @@ static void trim_stale_devices(struct pc
>  {
>  	struct acpi_device *adev = ACPI_COMPANION(&dev->dev);
>  	struct pci_bus *bus = dev->subordinate;
> -	bool alive = false;
> +	bool alive = dev->ignore_hotplug;
>  
>  	if (adev) {
>  		acpi_status status;
>  		unsigned long long sta;
>  
>  		status = acpi_evaluate_integer(adev->handle, "_STA", NULL, &sta);
> -		alive = (ACPI_SUCCESS(status) && device_status_valid(sta))
> -			|| dev->ignore_hotplug;
> +		alive = alive || (ACPI_SUCCESS(status) && device_status_valid(sta));
>  	}
>  	if (!alive)
>  		alive = pci_device_is_present(dev);
> 
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