linux-kernel - [tip: irq/urgent] genirq/cpuhotplug: Restore affinity even for suspended IRQ

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Message-ID: <174982054803.406.16499151161208578856.tip-bot2@tip-bot2>
Date: Fri, 13 Jun 2025 13:15:48 -0000
From: "tip-bot2 for Brian Norris" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Aleksandrs Vinarskis <alex.vinarskis@...il.com>,
 Brian Norris <briannorris@...omium.org>, Thomas Gleixner <tglx@...utronix.de>,
 x86@...nel.org, linux-kernel@...r.kernel.org, maz@...nel.org
Subject:
 [tip: irq/urgent] genirq/cpuhotplug: Restore affinity even for suspended IRQ

The following commit has been merged into the irq/urgent branch of tip:

Commit-ID:     72218d74c9c57b8ea36c2a58875dff406fc10462
Gitweb:        https://git.kernel.org/tip/72218d74c9c57b8ea36c2a58875dff406fc10462
Author:        Brian Norris <briannorris@...omium.org>
AuthorDate:    Thu, 12 Jun 2025 11:32:52 -07:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Fri, 13 Jun 2025 15:13:35 +02:00

genirq/cpuhotplug: Restore affinity even for suspended IRQ

Commit 788019eb559f ("genirq: Retain disable depth for managed interrupts
across CPU hotplug") tried to make managed shutdown/startup properly
reference counted, but it missed the fact that the unplug and hotplug code
has an intentional imbalance by skipping IRQS_SUSPENDED interrupts on
the "restore" path.

This means that if a managed-affinity interrupt was both suspended and
managed-shutdown (such as may happen during system suspend / S3), resume
skips calling irq_startup_managed(), and would again have an unbalanced
depth this time, with a positive value (i.e., remaining unexpectedly
masked).

This IRQS_SUSPENDED check was introduced in commit a60dd06af674
("genirq/cpuhotplug: Skip suspended interrupts when restoring affinity")
for essentially the same reason as commit 788019eb559f, to prevent that
irq_startup() would unconditionally re-enable an interrupt too early.

Because irq_startup_managed() now respsects the disable-depth count, the
IRQS_SUSPENDED check is not longer needed, and instead, it causes harm.

Thus, drop the IRQS_SUSPENDED check, and restore balance.

This effectively reverts commit a60dd06af674 ("genirq/cpuhotplug: Skip
suspended interrupts when restoring affinity"), because it is replaced
by commit 788019eb559f ("genirq: Retain disable depth for managed
interrupts across CPU hotplug").

Fixes: 788019eb559f ("genirq: Retain disable depth for managed interrupts across CPU hotplug")
Reported-by: Aleksandrs Vinarskis <alex.vinarskis@...il.com>
Signed-off-by: Brian Norris <briannorris@...omium.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Aleksandrs Vinarskis <alex.vinarskis@...il.com>
Link: https://lore.kernel.org/all/20250612183303.3433234-3-briannorris@chromium.org
Closes: https://lore.kernel.org/lkml/24ec4adc-7c80-49e9-93ee-19908a97ab84@gmail.com/
---
 kernel/irq/cpuhotplug.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/kernel/irq/cpuhotplug.c b/kernel/irq/cpuhotplug.c
index f07529a..755346e 100644
--- a/kernel/irq/cpuhotplug.c
+++ b/kernel/irq/cpuhotplug.c
@@ -210,13 +210,6 @@ static void irq_restore_affinity_of_irq(struct irq_desc *desc, unsigned int cpu)
 	    !irq_data_get_irq_chip(data) || !cpumask_test_cpu(cpu, affinity))
 		return;

-	/*
-	 * Don't restore suspended interrupts here when a system comes back
-	 * from S3. They are reenabled via resume_device_irqs().
-	 */
-	if (desc->istate & IRQS_SUSPENDED)
-		return;
-
 	if (irqd_is_managed_and_shutdown(data))
 		irq_startup_managed(desc);