linux.git/kernel/irq/chip.c, branch v6.16

genirq/cpuhotplug: Rebalance managed interrupts across multi-CPU hotplug

2025-06-13T13:13:35+00:00

Commit 788019eb559f ("genirq: Retain disable depth for managed interrupts
across CPU hotplug") intended to only decrement the disable depth once per
managed shutdown, but instead it decrements for each CPU hotplug in the
affinity mask, until its depth reaches a point where it finally gets
re-started.

For example, consider:

1. Interrupt is affine to CPU {M,N}
2. disable_irq() -> depth is 1
3. CPU M goes offline -> interrupt migrates to CPU N / depth is still 1
4. CPU N goes offline -> irq_shutdown() / depth is 2
5. CPU N goes online
    -> irq_restore_affinity_of_irq()
       -> irqd_is_managed_and_shutdown()==true
          -> irq_startup_managed() -> depth is 1
6. CPU M goes online
    -> irq_restore_affinity_of_irq()
       -> irqd_is_managed_and_shutdown()==true
          -> irq_startup_managed() -> depth is 0
          *** BUG: driver expects the interrupt is still disabled ***
             -> irq_startup() -> irqd_clr_managed_shutdown()
7. enable_irq() -> depth underflow / unbalanced enable_irq() warning

This should clear the managed-shutdown flag at step 6, so that further
hotplugs don't cause further imbalance.

Note: It might be cleaner to also remove the irqd_clr_managed_shutdown()
invocation from __irq_startup_managed(). But this is currently not possible
because of irq_update_affinity_desc() as it sets IRQD_MANAGED_SHUTDOWN and
expects irq_startup() to clear it.

Fixes: 788019eb559f ("genirq: Retain disable depth for managed interrupts across CPU hotplug")
Reported-by: Aleksandrs Vinarskis 
Signed-off-by: Brian Norris 
Signed-off-by: Thomas Gleixner 
Tested-by: Aleksandrs Vinarskis 
Link: https://lore.kernel.org/all/20250612183303.3433234-2-briannorris@chromium.org

genirq: Retain disable depth for managed interrupts across CPU hotplug

2025-05-15T14:44:25+00:00

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 
Signed-off-by: Brian Norris 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/all/20250514201353.3481400-2-briannorris@chromium.org

genirq: Fix inverted condition in handle_nested_irq()

2025-05-09T18:42:26+00:00

Marek reported that the rework of handle_nested_irq() introduced a inverted
condition, which prevents handling of interrupts. Fix it up.

Fixes: 2ef2e13094c7 ("genirq/chip: Rework handle_nested_irq()")
Reported-by: Marek Szyprowski 
Signed-off-by: Thomas Gleixner 
Closes: https://lore.kernel/org/all/46ed4040-ca11-4157-8bd7-13c04c113734@samsung.com

genirq/chip: Rework irq_modify_status()

2025-05-07T07:08:14+00:00

Use the new guards to get and lock the interrupt descriptor and tidy up the
code.

Fixup the kernel doc comment while at it.

No functional change.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/all/20250429065421.650454052@linutronix.de

genirq/chip: Rework irq_set_handler() variants

2025-05-07T07:08:14+00:00

Use the new guards to get and lock the interrupt descriptor and tidy up the
code.

Fixup the kernel doc comment while at it.

No functional change.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/all/20250429065421.590753128@linutronix.de

genirq/chip: Rework irq_set_chip_data()

2025-05-07T07:08:14+00:00

Use the new guards to get and lock the interrupt descriptor and tidy up the
code.

Fixup the kernel doc comment while at it.

No functional change.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/all/20250429065421.532308759@linutronix.de

genirq/chip: Rework irq_set_msi_desc_off()

2025-05-07T07:08:14+00:00

Use the new guards to get and lock the interrupt descriptor and tidy up the
code.

Fixup the kernel doc comment while at it.

No functional change.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/all/20250429065421.473563978@linutronix.de

genirq/chip: Rework irq_set_handler_data()

2025-05-07T07:08:14+00:00

Use the new guards to get and lock the interrupt descriptor and tidy up the
code.

Fixup the kernel doc comment while at it.

No functional change.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/all/20250429065421.415072350@linutronix.de

genirq/chip: Rework irq_set_irq_type()

2025-05-07T07:08:13+00:00

Use the new guards to get and lock the interrupt descriptor and tidy up the
code.

Fixup the kernel doc comment while at it.

No functional change.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/all/20250429065421.355673840@linutronix.de

genirq/chip: Rework irq_set_chip()

2025-05-07T07:08:13+00:00

Use the new guards to get and lock the interrupt descriptor and tidy up the
code.

Fixup the kernel doc comment while at it.

No functional change.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/all/20250429065421.295400891@linutronix.de