Re: [PATCH AUTOSEL 6.15 092/110] genirq: Retain disable depth for managed interrupts across CPU hotplug

[Sasha Levin]

On Fri, Jun 06, 2025 at 02:32:29PM +0200, Johan Hovold wrote:
> On Sun, Jun 01, 2025 at 07:24:14PM -0400, Sasha Levin wrote:
> > From: Brian Norris <briannorris@xxxxxxxxxxxx>
> >
> > [ Upstream commit 788019eb559fd0b365f501467ceafce540e377cc ]
> >
> > Affinity-managed interrupts can be shut down and restarted during CPU
> > hotunplug/plug. Thereby the interrupt may be left in an unexpected state.
> > Specifically:
> >
> >  1. Interrupt is affine to CPU N
> >  2. disable_irq() -> depth is 1
> >  3. CPU N goes offline
> >  4. irq_shutdown() -> depth is set to 1 (again)
> >  5. CPU N goes online
> >  6. irq_startup() -> depth is set to 0 (BUG! driver expects that the interrupt
> >     		     	      	        still disabled)
> >  7. enable_irq() -> depth underflow / unbalanced enable_irq() warning
> >
> > This is only a problem for managed interrupts and CPU hotplug, all other
> > cases like request()/free()/request() truly needs to reset a possibly stale
> > disable depth value.
> >
> > Provide a startup function, which takes the disable depth into account, and
> > invoked it for the managed interrupts in the CPU hotplug path.
> >
> > This requires to change irq_shutdown() to do a depth increment instead of
> > setting it to 1, which allows to retain the disable depth, but is harmless
> > for the other code paths using irq_startup(), which will still reset the
> > disable depth unconditionally to keep the original correct behaviour.
> >
> > A kunit tests will be added separately to cover some of these aspects.
> >
> > [ tglx: Massaged changelog ]
> >
> > Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
> > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Link: https://lore.kernel.org/all/20250514201353.3481400-2-briannorris@xxxxxxxxxxxx
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
>
> This one breaks suspend of laptops like the Lenovo ThinkPad T14s. Issue
> was just reported here by Alex:
>
> 	https://lore.kernel.org/lkml/24ec4adc-7c80-49e9-93ee-19908a97ab84@xxxxxxxxx/
>
> Please drop from all stable queues for now.

Will do, thanks!

--
Thanks,
Sasha