[PATCH] Support resetting WARN*_ONCE

[Andi Kleen]

From: Andi Kleen <ak@xxxxxxxxxxxxxxx>

I like _ONCE warnings because it's guaranteed that they don't
flood the log.

During testing I find it useful to reset the state of the once warnings,
so that I can rerun tests and see if they trigger again, or can
guarantee that a test run always hits the same warnings.

This patch adds a debugfs interface to reset all the _ONCE
warnings so that they appear again:

echo 1 > /sys/kernel/debug/clear_warn_once

This is implemented by putting all the warning booleans into
a special section, and clearing it.

Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
---
 include/asm-generic/bug.h         |  6 +++---
 include/asm-generic/sections.h    |  1 +
 include/asm-generic/vmlinux.lds.h |  3 +++
 kernel/panic.c                    | 27 +++++++++++++++++++++++++++
 4 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 87191357d303..68c2f08b7914 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -129,7 +129,7 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 
 #ifndef WARN_ON_ONCE
 #define WARN_ON_ONCE(condition)	({				\
-	static bool __section(.data.unlikely) __warned;		\
+	static bool __section(.data.once) __warned;		\
 	int __ret_warn_once = !!(condition);			\
 								\
 	if (unlikely(__ret_warn_once && !__warned)) {		\
@@ -141,7 +141,7 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 #endif
 
 #define WARN_ONCE(condition, format...)	({			\
-	static bool __section(.data.unlikely) __warned;		\
+	static bool __section(.data.once) __warned;		\
 	int __ret_warn_once = !!(condition);			\
 								\
 	if (unlikely(__ret_warn_once && !__warned)) {		\
@@ -152,7 +152,7 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 })
 
 #define WARN_TAINT_ONCE(condition, taint, format...)	({	\
-	static bool __section(.data.unlikely) __warned;		\
+	static bool __section(.data.once) __warned;		\
 	int __ret_warn_once = !!(condition);			\
 								\
 	if (unlikely(__ret_warn_once && !__warned)) {		\
diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index e5da44eddd2f..611c01bc5d21 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h
@@ -43,6 +43,7 @@ extern char __entry_text_start[], __entry_text_end[];
 extern char __start_rodata[], __end_rodata[];
 extern char __irqentry_text_start[], __irqentry_text_end[];
 extern char __softirqentry_text_start[], __softirqentry_text_end[];
+extern char __start_once[], __end_once[];
 
 /* Start and end of .ctors section - used for constructor calls. */
 extern char __ctors_start[], __ctors_end[];
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 8acfc1e099e1..ac511e24ea4a 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -223,6 +223,9 @@
 	MEM_KEEP(init.data)						\
 	MEM_KEEP(exit.data)						\
 	*(.data.unlikely)						\
+	VMLINUX_SYMBOL(__start_once) = .;				\
+	*(.data.once)							\
+	VMLINUX_SYMBOL(__end_once) = .;					\
 	STRUCT_ALIGN();							\
 	*(__tracepoints)						\
 	/* implement dynamic printk debug */				\
diff --git a/kernel/panic.c b/kernel/panic.c
index bdd18afa19a4..b2d872fa16de 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -27,6 +27,7 @@
 #include <linux/console.h>
 #include <linux/bug.h>
 #include <linux/ratelimit.h>
+#include <linux/debugfs.h>
 
 #define PANIC_TIMER_STEP 100
 #define PANIC_BLINK_SPD 18
@@ -587,6 +588,32 @@ void warn_slowpath_null(const char *file, int line)
 EXPORT_SYMBOL(warn_slowpath_null);
 #endif
 
+#ifdef CONFIG_BUG
+
+/* Support resetting WARN*_ONCE state */
+
+static int clear_warn_once_set(void *data, u64 val)
+{
+	memset(__start_once, 0, __end_once - __start_once);
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(clear_warn_once_fops,
+			NULL,
+                        clear_warn_once_set,
+		        "%lld\n");
+
+static __init int register_warn_debugfs(void)
+{
+	/* Don't care about failure */
+	debugfs_create_file("clear_warn_once", 0644, NULL,
+			    NULL, &clear_warn_once_fops);
+	return 0;
+}
+
+__initcall(register_warn_debugfs);
+#endif
+
 #ifdef CONFIG_CC_STACKPROTECTOR
 
 /*
-- 
2.13.6