linux-kernel - Re: [PATCH 8/9] PCI / ACPI / PM: Platform support for PCI PME wake-up (rev. 7)

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Message-Id: <201002130120.29385.rjw@sisk.pl>
Date:	Sat, 13 Feb 2010 01:20:29 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Gary Hade <garyhade@...ibm.com>
Cc:	linux-pm@...ts.linux-foundation.org,
	Linux PCI <linux-pci@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"Moore, Robert" <robert.moore@...el.com>,
	Matthew Garrett <mjg@...hat.com>,
	Bjorn Helgaas <bjorn.helgaas@...com>
Subject: Re: [PATCH 8/9] PCI / ACPI / PM: Platform support for PCI PME wake-up (rev. 7)

On Friday 12 February 2010, Rafael J. Wysocki wrote:
> On Friday 12 February 2010, Gary Hade wrote:
... 
> > There seems to be a problem.
> > 
> > The first time I booted I was able to successfully hot-remove
> > a PCIe card and then successfully hot-add it to a different slot.
> > When I tried to hot-remove a PCI-X card that was also present
> > during boot I saw that lingering blinking amber LED issue.
> > 
> > After rebooting I tried the same thing but this time I did
> > not see the lingering blinking amber LED after removing the
> > PCI-X card but I did see it when removing the PCIe card.
> > I then tried to hot-add the PCIe card to a different slot
> > and noticed the below messages.
> > 
> > I don't think I will be able to try to characterize this
> > better or test any more patches until Monday.  
> 
> OK, thanks for testing.
> 
> It seems we have a deadlock on pci_acpi_notify_mtx, but I'm yet to understand
> the exact mechanism of it.

In fact there are two problems in there.  First, the bridge event notification
calls handle_bridge_insertion() which attempts to install a PM notifier for
the bridge and that deadlocks, because it tries to acquire the mutex
recursively.  Second, apparently, init_bridge_misc() may be called in the
notification code path and it attempts to unregister the notifier and register
it again, which can't be done with pci_acpi_notify_mtx held.

I guess there are similar problems on the hot remove notification path.

Anyway, I have a new version of the patch and I'm going to test it a bit
over the weekend.  Unfortunately, I don't have hardware with PCI hotplug
capability, so I'll send you the new patch for testing on Monday, if you don't
mind.

Rafael
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