Date: Wed, 13 Dec 2017 21:52:34 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
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
Subject: Re: Linux 4.15-rc2: Regression in resume from ACPI S3
In-Reply-To: <alpine.DEB.2.20.1712131856130.1885@nanos>
Message-ID: <alpine.DEB.2.20.1712132149420.1885@nanos>
References: <168050887.sZlTFXWCmO@aspire.rjw.lan> <CA+55aFwsMuHUBQz5kDNwRf17JnasXMWjvmLq5qXGH-694yeq1w@mail.gmail.com> <20171206121452.GA6320@dhcp22.suse.cz> <db81e89d-eee6-868c-dc10-c028f4c4be84@mblankhorst.nl> <alpine.DEB.2.20.1712061344560.1724@nanos>
 <0f1d3d63-fa10-5cef-8014-81753dc60243@mblankhorst.nl> <alpine.DEB.2.20.1712061514420.1724@nanos> <57c8679e-1b88-c9ad-2299-2bea7560b28f@mblankhorst.nl> <alpine.DEB.2.20.1712081129450.1840@nanos> <alpine.DEB.2.20.1712131507160.1885@nanos>
 <20171213162336.GG53955@bhelgaas-glaptop.roam.corp.google.com> <alpine.DEB.2.20.1712131738020.1885@nanos> <CA+55aFw-SZLey5FaQfSLSbDU1sYhoGDrWoOngswkHMFfHW3O6w@mail.gmail.com> <alpine.DEB.2.20.1712131856130.1885@nanos>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1355
Lines: 31

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