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

[Thomas Gleixner]

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@xxxxxxxxxxxxx> 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