From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Linux 4.15-rc2: Regression in resume from ACPI S3
Date: Wed, 13 Dec 2017 21:52:34 +0100 (CET)
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Bjorn Helgaas <helgaas@kernel.org>, Maarten Lankhorst <dev@mblankhorst.nl>, Michal Hocko <mhocko@kernel.org>, "Rafael J. Wysocki" <rjw@rjwysocki.net>, Andy Lutomirski <luto@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, the arch/x86 maintainers <x86@kernel.org>, Daniel Vetter <daniel.vetter@intel.com>, Bjorn Helgaas <bhelgaas@google.com>, "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>, linux-pci@vger.kernel.org, linux-pm@vger.kernel.org
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On Wed, 13 Dec 2017, Thomas Gleixner wrote:
> On Wed, 13 Dec 2017, Linus Torvalds wrote:
> 
> > On Wed, Dec 13, 2017 at 8:41 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > >
> > > Definitely. That was fragile forever but puzzles me is that I can't figure
> > > out what now causes that spurious interrupt to surface out of the blue.
> > 
> > Perhaps just timing?
> 
> That's what I'm trying to figure out right now, because that is the only
> sensible explanation left. The whole machinery of suspend is exactly the
> same with and without the vector changes. I instrumented all functions
> involved and the picture is the same. I even do not see any fundamental
> timing differences where one would say: That's it.
> 
> What puzzles me even more is that in the range of commits I'm fiddling with
> there is no other change than the vector management stuff and the point
> where it breaks makes no sense at all. The point Maarten bisected it to
> works nicely here, so that might just point to a very subtle timing issue.

After doing more debugging on this it turns out that this looks like a
legacy interrupt coming in. The vector number is always 55, which is legacy
IRQ 7 as seen from the PIC. The corresponding IOAPIC interrupt pin is
masked and vector 55 is completely unused.

More questions than answers. Still investigating.

Thanks,

	tglx