linux-kernel - Re: Linux 4.15-rc2: Regression in resume from ACPI S3

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Date:   Wed, 13 Dec 2017 23:39:24 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Maarten Lankhorst <dev@...ankhorst.nl>,
        Michal Hocko <mhocko@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-pci@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: Linux 4.15-rc2: Regression in resume from ACPI S3

On Wednesday, December 13, 2017 7:19:17 PM CET Thomas Gleixner wrote:
> On Wed, 13 Dec 2017, Linus Torvalds wrote:
> 
> > On Wed, Dec 13, 2017 at 8:41 AM, Thomas Gleixner <tglx@...utronix.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.
> 
> > How hard would it be to change the ordering to just redirect irqs first?
> 
> The whole interrupt redirection happens when the non boot CPUs are brought
> down, which is the very last step before the actual suspend happens.
> 
> We could probably do that earlier, but that's something Rafael needs to
> answer ultimately.

Well, that's both flattering and concerning. ;-)

Anyway, yes, we can do that earlier AFAICS.  Action handlers are not going to
run after we've called suspend_device_irqs() which happens before the final
stage of PCI devices suspend (suspend_noirq) and it doesn't matter which CPU
gets the interrupt from that point on (it is either wakeup or unwanted then).

Thanks,
Rafael