[patch V4 12/15] genirq: Add rcuref count to struct irq_desc

Thomas Gleixner
2026-03-31T07:26:29Z

Prepare for a smarter iterator for /proc/interrupts so that the next
interrupt descriptor can be cached after lookup.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Dmitry Ilvokhin <d@ilvokhin.com>

---
include/linux/irqdesc.h | 2 ++
kernel/irq/internals.h | 17 ++++++++++++++++-
kernel/irq/irqdesc.c | 21 +++++++++++++--------
3 files changed, 31 insertions(+), 9 deletions(-)
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -70,6 +70,7 @@ struct irq_redirect {
* IRQF_NO_SUSPEND set
* @force_resume_depth: number of irqactions on a irq descriptor with
* IRQF_FORCE_RESUME set
+ * @refcnt: Reference count mainly for /proc/interrupts
* @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
@@ -119,6 +120,7 @@ struct irq_desc {
struct dentry *debugfs_file;
const char *dev_name;
#endif
+ rcuref_t refcnt;
#ifdef CONFIG_SPARSE_IRQ
struct rcu_head rcu;
struct kobject kobj;
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -9,6 +9,7 @@
#include <linux/irqdesc.h>
#include <linux/kernel_stat.h>
#include <linux/pm_runtime.h>
+#include <linux/rcuref.h>
#include <linux/sched/clock.h>

#ifdef CONFIG_SPARSE_IRQ
@@ -101,9 +102,23 @@ extern void unmask_irq(struct irq_desc *
extern void unmask_threaded_irq(struct irq_desc *desc);

#ifdef CONFIG_SPARSE_IRQ
-static inline void irq_mark_irq(unsigned int irq) { }
+static __always_inline void irq_mark_irq(unsigned int irq) { }
+void irq_desc_free_rcu(struct irq_desc *desc);
+
+static __always_inline bool irq_desc_get_ref(struct irq_desc *desc)
+{
+ return rcuref_get(&desc->refcnt);
+}
+
+static __always_inline void irq_desc_put_ref(struct irq_desc *desc)
+{
+ if (rcuref_put(&desc->refcnt))
+ irq_desc_free_rcu(desc);
+}
#else
extern void irq_mark_irq(unsigned int irq);
+static __always_inline bool irq_desc_get_ref(struct irq_desc *desc) { return true; }
+static __always_inline void irq_desc_put_ref(struct irq_desc *desc) { }
#endif

irqreturn_t __handle_irq_event_percpu(struct irq_desc *desc);
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -137,6 +137,7 @@ static void desc_set_defaults(unsigned i
desc->tot_count = 0;
desc->name = NULL;
desc->owner = owner;
+ rcuref_init(&desc->refcnt, 1);
desc_smp_init(desc, node, affinity);
}

@@ -465,6 +466,17 @@ static void delayed_free_desc(struct rcu
kobject_put(&desc->kobj);
}

+void irq_desc_free_rcu(struct irq_desc *desc)
+{
+ /*
+ * We free the descriptor, masks and stat fields via RCU. That
+ * allows demultiplex interrupts to do rcu based management of
+ * the child interrupts.
+ * This also allows us to use rcu in kstat_irqs_usr().
+ */
+ call_rcu(&desc->rcu, delayed_free_desc);
+}
+
static void free_desc(unsigned int irq)
{
struct irq_desc *desc = irq_to_desc(irq);
@@ -483,14 +495,7 @@ static void free_desc(unsigned int irq)
*/
irq_sysfs_del(desc);
delete_irq_desc(irq);
-
- /*
- * We free the descriptor, masks and stat fields via RCU. That
- * allows demultiplex interrupts to do rcu based management of
- * the child interrupts.
- * This also allows us to use rcu in kstat_irqs_usr().
- */
- call_rcu(&desc->rcu, delayed_free_desc);
+ irq_desc_put_ref(desc);
}

static int alloc_descs(unsigned int start, unsigned int cnt, int node,