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Date: Tue, 19 Nov 2013 22:10:06 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Toshi Kani <toshi.kani@...com>
Cc: ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Linux PCI <linux-pci@...r.kernel.org>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH 2/3] ACPI / hotplug: Fix PCI host bridge hot removal
> On Tuesday, November 19, 2013 10:48:51 AM Toshi Kani wrote:
> > On Mon, 2013-11-18 at 22:39 +0100, Rafael J. Wysocki wrote:
> > > On Monday, November 18, 2013 11:10:05 AM Toshi Kani wrote:
> > > > On Thu, 2013-11-14 at 00:16 +0100, Rafael J. Wysocki wrote:
> > > > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > > >
> > > > > Since the PCI host bridge scan handler does not set hotplug.enabled,
> > > > > the check of it in acpi_bus_device_eject() effectively prevents the
> > > > > root bridge hot removal from working after commit a3b1b1ef78cd
> > > > > (ACPI / hotplug: Merge device hot-removal routines). However, that
> > > > > check is not necessary, because the other acpi_bus_device_eject()
> > > > > users, acpi_hotplug_notify_cb and acpi_eject_store(), do the same
> > > > > check by themselves before executing that function.
> > > > >
> > > > > For this reason, remove the scan handler check from
> > > > > acpi_bus_device_eject() to make PCI hot bridge hot removal work
> > > > > again.
> > > >
> > > > I am curious why the PCI host bridge scan handler does not set
> > > > hotplug.enabled. Is this how it disables hotplug via sysfs eject but
> > > > enables via ACPI notification?
> > >
> > > It just doesn't register for hotplug at all. I guess it could set that
> > > bit alone, but then it would be quite confusing and the check is not
> > > necessary anyway.
> >
> > I see. Given how the PCI host bridge scan handler is integrated today,
> > the change looks reasonable to me.
>
> Looking further, I noticed that there is one more issue to address. The
> patch below applies on top of your patchset.
>
> From: Toshi Kani <toshi.kani@...com>
> Subject: [PATCH] ACPI / hotplug: Fix conflicted PCI bridge notify
> handlers
>
> The PCI host bridge scan handler installs its own notify handler,
> handle_hotplug_event_root(), by itself. Nevertheless, the ACPI
> hotplug framework also installs the common notify handler,
> acpi_hotplug_notify_cb(), for PCI root bridges. This causes
> acpi_hotplug_notify_cb() to call _OST method with unsupported
> error as hotplug.enabled is not set.
>
> To address this issue, introduce hotplug.self_install flag, which
> indicates that the scan handler installs its own notify handler by
> itself. The ACPI hotplug framework does not install the common
> notify handler when this flag is set.
Good catch!
Still, I don't think we need a new flag, because we know that that
scan handler doesn't support hotplug, because its hotplug profile
hasn't been registered (that actually applies to all scan handlers
without hotplug support, not only the root host bridge). Moreover,
if it does support hotplug, but the hotplug profile hasn't been
registered due to an error, we still should not install the notify
handler I think. So, I prefer the patch below.
And this fix will remain useful after my recent series at
http://marc.info/?l=linux-pci&m=138470560909690&w=4
Thanks,
Rafael
---
From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Subject: ACPI / hotplug: Ignore notifications for scan handlers without hotplug
If a scan handler's hotplug profile has not been registered, do not
install acpi_hotplug_notify_cb() as a notify handler for devices
with the given scan handler attached.
This fixes a problem with the PCI host bridge scan handler that
installs its own notify handler, handle_hotplug_event_root(), by
itself and doesn't register its hotplug profile. Toshi says
"Nevertheless, the ACPI hotplug framework also installs the common
notify handler, acpi_hotplug_notify_cb(), for PCI root bridges.
This causes acpi_hotplug_notify_cb() to call _OST method with
unsupported error as hotplug.enabled is not set."
Moreover, it is pointless to install acpi_hotplug_notify_cb() as
a notify handler for device objects whose scan handlers don't
support hotplug, because it will always fail for them.
Reported-by: Toshi Kani <toshi.kani@...com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Cc: 3.9+ <stable@...r.kernel.org> # 3.9+
---
drivers/acpi/scan.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
Index: linux-pm/drivers/acpi/scan.c
===================================================================
--- linux-pm.orig/drivers/acpi/scan.c
+++ linux-pm/drivers/acpi/scan.c
@@ -84,6 +84,11 @@ int acpi_scan_add_handler_with_hotplug(s
return 0;
}
+static bool acpi_scan_handler_with_hotplug(struct acpi_scan_handler *handler)
+{
+ return handler && handler->hotplug.kobj.state_in_sysfs;
+}
+
/*
* Creates hid/cid(s) string needed for modalias and uevent
* e.g. on a device with hid:IBM0001 and cid:ACPI0001 you get:
@@ -1841,7 +1846,7 @@ static void acpi_scan_init_hotplug(acpi_
*/
list_for_each_entry(hwid, &pnp.ids, list) {
handler = acpi_scan_match_handler(hwid->id, NULL);
- if (handler) {
+ if (acpi_scan_handler_with_hotplug(handler)) {
acpi_install_notify_handler(handle, ACPI_SYSTEM_NOTIFY,
acpi_hotplug_notify_cb, handler);
break;
--
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