linux-kernel - [tip: irq/core] genirq: Retain disable depth for managed interrupts across CPU hotplug

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Message-ID: <174732070271.406.3712146055779909597.tip-bot2@tip-bot2>
Date: Thu, 15 May 2025 14:51:42 -0000
From: "tip-bot2 for Brian Norris" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
 Brian Norris <briannorris@...omium.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org, maz@...nel.org
Subject: [tip: irq/core] genirq: Retain disable depth for managed interrupts
 across CPU hotplug

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

Commit-ID:     788019eb559fd0b365f501467ceafce540e377cc
Gitweb:        https://git.kernel.org/tip/788019eb559fd0b365f501467ceafce540e377cc
Author:        Brian Norris <briannorris@...omium.org>
AuthorDate:    Wed, 14 May 2025 13:13:16 -07:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 15 May 2025 16:44:25 +02:00

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: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Brian Norris <briannorris@...omium.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/all/20250514201353.3481400-2-briannorris@chromium.org
---
 kernel/irq/chip.c       | 22 +++++++++++++++++++++-
 kernel/irq/cpuhotplug.c |  2 +-
 kernel/irq/internals.h  |  1 +
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index 1d45c84..b0e0a73 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -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);
diff --git a/kernel/irq/cpuhotplug.c b/kernel/irq/cpuhotplug.c
index e77ca6d..f07529a 100644
--- a/kernel/irq/cpuhotplug.c
+++ b/kernel/irq/cpuhotplug.c
@@ -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
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index 476a20f..aebfe22 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -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);