Commit 788019eb authored by Brian Norris's avatar Brian Norris Committed by Thomas Gleixner
Browse files

genirq: Retain disable depth for managed interrupts across CPU hotplug 



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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarBrian Norris <briannorris@chromium.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250514201353.3481400-2-briannorris@chromium.org
parent a4a39c81

kernel/irq/chip.c

+21 −1
Original line number Diff line number Diff line
@@ -202,6 +202,19 @@ __irq_startup_managed(struct irq_desc *desc, const struct cpumask *aff, 
		return IRQ_STARTUP_ABORT;

	return IRQ_STARTUP_MANAGED;

}



void irq_startup_managed(struct irq_desc *desc)

{

	/*

	 * Only start it up when the disable depth is 1, so that a disable,

	 * hotunplug, hotplug sequence does not end up enabling it during

	 * hotplug unconditionally.

	 */

	desc->depth--;

	if (!desc->depth)

		irq_startup(desc, IRQ_RESEND, IRQ_START_COND);

}



#else

static __always_inline int

__irq_startup_managed(struct irq_desc *desc, const struct cpumask *aff,
@@ -269,6 +282,7 @@ int irq_startup(struct irq_desc *desc, bool resend, bool force) 
			ret = __irq_startup(desc);

			break;

		case IRQ_STARTUP_ABORT:

			desc->depth = 1;

			irqd_set_managed_shutdown(d);

			return 0;

		}
@@ -301,7 +315,13 @@ void irq_shutdown(struct irq_desc *desc) 
{

	if (irqd_is_started(&desc->irq_data)) {

		clear_irq_resend(desc);

		desc->depth = 1;

		/*

		 * Increment disable depth, so that a managed shutdown on

		 * CPU hotunplug preserves the actual disabled state when the

		 * CPU comes back online. See irq_startup_managed().

		 */

		desc->depth++;



		if (desc->irq_data.chip->irq_shutdown) {

			desc->irq_data.chip->irq_shutdown(&desc->irq_data);

			irq_state_set_disabled(desc);

kernel/irq/cpuhotplug.c

+1 −1
Original line number Diff line number Diff line
@@ -218,7 +218,7 @@ static void irq_restore_affinity_of_irq(struct irq_desc *desc, unsigned int cpu) 
		return;



	if (irqd_is_managed_and_shutdown(data))

		irq_startup(desc, IRQ_RESEND, IRQ_START_COND);

		irq_startup_managed(desc);



	/*

	 * If the interrupt can only be directed to a single target

kernel/irq/internals.h

+1 −0
Original line number Diff line number Diff line
@@ -87,6 +87,7 @@ extern void __enable_irq(struct irq_desc *desc); 
extern int irq_activate(struct irq_desc *desc);

extern int irq_activate_and_startup(struct irq_desc *desc, bool resend);

extern int irq_startup(struct irq_desc *desc, bool resend, bool force);

extern void irq_startup_managed(struct irq_desc *desc);



extern void irq_shutdown(struct irq_desc *desc);

extern void irq_shutdown_and_deactivate(struct irq_desc *desc);