linux-kernel - [PATCH 2/5] irqdesc: Use dynamic lockdep keys for interrupt descriptors

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Message-ID: <20250203175939.3133477-3-bvanassche@acm.org>
Date: Mon,  3 Feb 2025 09:59:36 -0800
From: Bart Van Assche <bvanassche@....org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Bart Van Assche <bvanassche@....org>
Subject: [PATCH 2/5] irqdesc: Use dynamic lockdep keys for interrupt descriptors

Having to call irq_set_lockdep_class() if nested locking is expected is
cumbersome. Hence, prepare for removing irq_set_lockdep_class() by
associating a dynamic key with the synchronization objects in interrupt
descriptors.

Signed-off-by: Bart Van Assche <bvanassche@....org>
---
 include/linux/irqdesc.h |  4 ++++
 kernel/irq/irqdesc.c    | 22 +++++++++-------------
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index fd091c35d572..5f4bd476fcc8 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -46,6 +46,7 @@ struct irqstat {
  * @threads_handled:	stats field for deferred spurious detection of threaded handlers
  * @threads_handled_last: comparator field for deferred spurious detection of threaded handlers
  * @lock:		locking for SMP
+ * @lock_key:		Lockdep class for @lock
  * @affinity_hint:	hint to user space for preferred irq affinity
  * @affinity_notify:	context for notification of affinity changes
  * @pending_mask:	pending rebalanced interrupts
@@ -60,6 +61,7 @@ struct irqstat {
  * @rcu:		rcu head for delayed free
  * @kobj:		kobject used to represent this struct in sysfs
  * @request_mutex:	mutex to protect request/free before locking desc->lock
+ * @request_key:	Lockdep class for @request_mutex
  * @dir:		/proc/irq/ procfs entry
  * @debugfs_file:	dentry for the debugfs file
  * @name:		flow handler name for /proc/interrupts output
@@ -81,6 +83,7 @@ struct irq_desc {
 	atomic_t		threads_handled;
 	int			threads_handled_last;
 	raw_spinlock_t		lock;
+	struct lock_class_key	lock_key;
 	struct cpumask		*percpu_enabled;
 	const struct cpumask	*percpu_affinity;
 #ifdef CONFIG_SMP
@@ -111,6 +114,7 @@ struct irq_desc {
 	struct kobject		kobj;
 #endif
 	struct mutex		request_mutex;
+	struct lock_class_key	request_key;
 	int			parent_irq;
 	struct module		*owner;
 	const char		*name;
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 287830739783..261305a213fd 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -19,11 +19,6 @@
 
 #include "internals.h"
 
-/*
- * lockdep: we want to handle all irq_desc locks as a single lock-class:
- */
-static struct lock_class_key irq_desc_lock_class;
-
 #if defined(CONFIG_SMP)
 static int __init irq_affinity_setup(char *str)
 {
@@ -222,8 +217,11 @@ static int init_desc(struct irq_desc *desc, int irq, int node,
 	}
 
 	raw_spin_lock_init(&desc->lock);
-	lockdep_set_class(&desc->lock, &irq_desc_lock_class);
+	lockdep_register_key(&desc->lock_key);
+	lockdep_set_class(&desc->lock, &desc->lock_key);
 	mutex_init(&desc->request_mutex);
+	lockdep_register_key(&desc->request_key);
+	lockdep_set_class(&desc->lock, &desc->request_key);
 	init_waitqueue_head(&desc->wait_for_threads);
 	desc_set_defaults(irq, desc, node, affinity, owner);
 	irqd_set(&desc->irq_data, flags);
@@ -484,13 +482,17 @@ static struct irq_desc *alloc_desc(int irq, int node, unsigned int flags,
 	return desc;
 }
 
+/* Called from RCU context. Hence, must not sleep. */
 static void irq_kobj_release(struct kobject *kobj)
 {
 	struct irq_desc *desc = container_of(kobj, struct irq_desc, kobj);
 
 	free_masks(desc);
 	free_percpu(desc->kstat_irqs);
-	kfree(desc);
+	lockdep_unregister_key_nosync(&desc->request_key);
+	lockdep_unregister_key_nosync(&desc->lock_key);
+	init_rcu_head(&desc->rcu);
+	kfree_rcu(desc, rcu);
 }
 
 static void delayed_free_desc(struct rcu_head *rhp)
@@ -1064,12 +1066,6 @@ unsigned int kstat_irqs_usr(unsigned int irq)
 void __irq_set_lockdep_class(unsigned int irq, struct lock_class_key *lock_class,
 			     struct lock_class_key *request_class)
 {
-	struct irq_desc *desc = irq_to_desc(irq);
-
-	if (desc) {
-		lockdep_set_class(&desc->lock, lock_class);
-		lockdep_set_class(&desc->request_mutex, request_class);
-	}
 }
 EXPORT_SYMBOL_GPL(__irq_set_lockdep_class);
 #endif