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

[Johan Hovold]

On Sun, Jun 01, 2025 at 07:24:14PM -0400, Sasha Levin wrote:
> From: Brian Norris <briannorris at chromium.org>
> 
> [ 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 at linutronix.de>
> Signed-off-by: Brian Norris <briannorris at chromium.org>
> Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
> Link: https://lore.kernel.org/all/20250514201353.3481400-2-briannorris@chromium.org
> Signed-off-by: Sasha Levin <sashal at kernel.org>

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@gmail.com/

Please drop from all stable queues for now.

Johan