Re: [PATCH 05/24] irq & spin_lock: Add counted interrupt disabling/enabling

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Aug 03, 2026 at 11:29:10AM +0200, Peter Zijlstra wrote:
> On Fri, Jul 31, 2026 at 01:30:06PM -0700, Boqun Feng wrote:
> > +++ b/include/linux/interrupt_rc.h
> > @@ -0,0 +1,67 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * include/linux/interrupt_rc.h - refcounted local processor interrupt
> > + * management.
> > + *
> > + * Since the implementation of this API currently depends on
> > + * local_irq_save()/local_irq_restore(), we split this into it's own header to
> > + * make it easier to include without hitting circular header dependencies.
> > + */
> > +
> > +#ifndef __LINUX_INTERRUPT_RC_H
> > +#define __LINUX_INTERRUPT_RC_H
> > +
> > +#include <linux/irqflags.h>
> > +#include <asm/processor.h>
> > +#ifdef CONFIG_SMP
> > +#include <asm/smp.h>
> > +#endif
> > +
> > +/* Per-cpu interrupt disabling state for local_interrupt_{disable,enable}() */
> > +struct interrupt_disable_state {
> > +	unsigned long flags;
> > +};
> > +
> > +DECLARE_PER_CPU(struct interrupt_disable_state, local_interrupt_disable_state);
> 
> I'm a bit confused by the need for this struct; afaict there aren't any
> additional members in the rest of the series. So at this point this is
> pointless wrappery, no?
> 
> Having this variable exported is unfortunate.

One option to get rid of that EXPORT would be something like so I
suppose.

---
--- a/include/linux/interrupt_rc.h
+++ b/include/linux/interrupt_rc.h
@@ -12,21 +12,52 @@
 #define __LINUX_INTERRUPT_RC_H
 
 #include <linux/irqflags.h>
+#include <linux/preempt.h>
 #include <asm/processor.h>
 #ifdef CONFIG_SMP
 #include <asm/smp.h>
 #endif
 
+#ifndef MODULE
 /* Per-cpu interrupt disabling state for local_interrupt_{disable,enable}() */
-struct interrupt_disable_state {
+DECLARE_PER_CPU(unsigned long, local_interrupt_disable_state);
+
+static __always_inline void __local_interrupt_disable(void)
+{
 	unsigned long flags;
-};
 
-DECLARE_PER_CPU(struct interrupt_disable_state, local_interrupt_disable_state);
+	local_irq_save(flags);
+	raw_cpu_write(local_interrupt_disable_state, flags);
+}
+
+static __always_inline void __local_interrupt_enable(void)
+{
+	unsigned long flags = raw_cpu_read(local_interrupt_disable_state);
+	local_irq_restore(flags);
+}
+
+#ifndef INSTANTIATE_EXPORTED_INTERRUPT_DISABLE
+static __always_inline void _local_interrupt_disable(void)
+{
+	__local_interrupt_disable();
+}
+
+static __always_inline void _local_interrupt_enable(void)
+{
+	__local_interrupt_enable();
+}
+#else
+extern void _local_interrupt_disable(void);
+extern void _local_interrupt_enable(void);
+#endif
+
+#else /* !MODULE */
+extern void _local_interrupt_disable(void);
+extern void _local_interrupt_enable(void);
+#endif /* !MODULE */
 
 static inline void local_interrupt_disable(void)
 {
-	unsigned long flags;
 	unsigned long new_count;
 
 	WARN_ON_ONCE(in_nmi());
@@ -35,10 +66,8 @@ static inline void local_interrupt_disab
 
 	/* Interrupts can happen here, but it's OK, see __irq_exit_rcu(). */
 
-	if ((new_count & HARDIRQ_DISABLE_MASK) == HARDIRQ_DISABLE_OFFSET) {
-		local_irq_save(flags);
-		raw_cpu_write(local_interrupt_disable_state.flags, flags);
-	}
+	if ((new_count & HARDIRQ_DISABLE_MASK) == HARDIRQ_DISABLE_OFFSET)
+		_local_interrupt_disable();
 }
 
 #ifdef CONFIG_PREEMPTION
@@ -63,14 +92,8 @@ static inline void local_interrupt_enabl
 
 	new_count = hardirq_disable_exit();
 
-	if ((new_count & HARDIRQ_DISABLE_MASK) == 0) {
-		unsigned long flags;
-
-		flags = raw_cpu_read(local_interrupt_disable_state.flags);
-		local_irq_restore(flags);
-
-		local_interrupt_enable_reched(new_count);
-	}
+	if ((new_count & HARDIRQ_DISABLE_MASK) == 0)
+		_local_interrupt_enable();
 }
 
 #endif /* !__LINUX_INTERRUPT_RC_H */
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -9,6 +9,7 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#define INSTANTIATE_EXPORTED_INTERRUPT_DISABLE
 #include <linux/export.h>
 #include <linux/kernel_stat.h>
 #include <linux/interrupt.h>
@@ -88,8 +89,17 @@ EXPORT_PER_CPU_SYMBOL_GPL(hardirqs_enabl
 EXPORT_PER_CPU_SYMBOL_GPL(hardirq_context);
 #endif
 
-DEFINE_PER_CPU(struct interrupt_disable_state, local_interrupt_disable_state);
-EXPORT_PER_CPU_SYMBOL_GPL(local_interrupt_disable_state);
+DEFINE_PER_CPU(unsigned long, local_interrupt_disable_state);
+
+void _local_interrupt_disable(void)
+{
+	__local_interrupt_disable();
+}
+
+void _local_interrupt_enable(void)
+{
+	__local_interrupt_enable();
+}
 
 #ifndef CONFIG_HAS_SEPARATE_PREEMPT_RESCHED_BITS
 /*