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

From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Bjorn Helgaas <helgaas@kernel.org>,
	Maarten Lankhorst <dev@mblankhorst.nl>,
	Michal Hocko <mhocko@kernel.org>,
	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 <linux-pci@vger.kernel.org>,
	Linux PM <linux-pm@vger.kernel.org>
Subject: Re: Linux 4.15-rc2: Regression in resume from ACPI S3
Date: Thu, 14 Dec 2017 00:26:32 +0100	[thread overview]
Message-ID: <CAJZ5v0g1bGtHiWoOVpj6-zYcLsici=jdoq-AFrRwnSAH7dXurQ@mail.gmail.com> (raw)
In-Reply-To: <2011671.y8uyto1vn5@aspire.rjw.lan>

On Wed, Dec 13, 2017 at 11:39 PM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> 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@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.
>>
>> > 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).

There is a catch that we don't and likely should not do that for
suspend-to-idle, but since we have pm_suspend_target_state now, that
case can be distinguished from the "full suspend" one readily.

Thanks,
Rafael