[RFC 7/8] x86/bug: Implement WARN_ONCE()

Peter Zijlstra
2025-06-02T14:50:44Z

Implement WARN_ONCE like WARN using BUGFLAG_ONCE.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/bug.h | 28 ++++++++++++++++++++++++++++
include/asm-generic/bug.h | 2 ++
2 files changed, 30 insertions(+)

--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -221,6 +221,34 @@ do { \
#define __WARN_printf(taint, fmt, arg...) \
CONCATENATE(__WARN_printf_, WARN_ARGS(arg))(BUGFLAG_TAINT(taint), fmt, ## arg)

+#define __WONCE_printf_0(flags, format) \
+ __WARN_printf_0(flags|BUGFLAG_ONCE, format)
+
+#define __WONCE_printf_1(flags, format, arg1) \
+ __WARN_printf_1(flags|BUGFLAG_ONCE, format, arg1)
+
+#define __WONCE_printf_2(flags, format, arg1, arg2) \
+ __WARN_printf_2(flags|BUGFLAG_ONCE, format, arg1, arg2)
+
+#define __WONCE_printf_3(flags, format, arg1, arg2, arg3) \
+ __WARN_printf_3(flags|BUGFLAG_ONCE, format, arg1, arg2, arg3)
+
+#define __WONCE_printf_n(flags, format, arg...) \
+ if (__ONCE_LITE_IF(true)) __WARN_printf_n(flags, format, arg)
+
+#define _WARN_ONCE(cond, format, arg...) ({ \
+ int __ret_warn_on = !!(cond); \
+ if (unlikely(__ret_warn_on)) { \
+ CONCATENATE(__WONCE_printf_, WARN_ARGS(arg))(0, format, ## arg); \
+ } \
+ __ret_warn_on; \
+})
+
+/*
+ * Make sure WARN_ONCE() arguments get expanded before trying to count them.
+ */
+#define WARN_ONCE(cond, format...) _WARN_ONCE(cond, format)
+
#endif /* HAVE_ARCH_BUG_FORMAT */

#include <asm-generic/bug.h>
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -155,8 +155,10 @@ extern __printf(1, 2) void __warn_printk
DO_ONCE_LITE_IF(condition, WARN_ON, 1)
#endif

+#ifndef WARN_ONCE
#define WARN_ONCE(condition, format...) \
DO_ONCE_LITE_IF(condition, WARN, 1, format)
+#endif

#define WARN_TAINT_ONCE(condition, taint, format...) \
DO_ONCE_LITE_IF(condition, WARN_TAINT, 1, taint, format)