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genirq: Retain disable depth for managed interrupts across CPU hotplug

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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@linutronix.de>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250514201353.3481400-2-briannorris@chromium.org
This commit is contained in:
Brian Norris 2025-05-14 13:13:16 -07:00 • committed by Thomas Gleixner
parent a4a39c81e1
commit 788019eb55
3 changed files with 23 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

22
kernel/irq/chip.c
View file

@ -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);

2
kernel/irq/cpuhotplug.c
View file

@ -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

1
kernel/irq/internals.h
View file

@ -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);