[PATCH] Support resetting WARN*_ONCE

Andi Kleen
2017-10-17T21:40:26Z

From: Andi Kleen <ak@linux.intel.com>

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@linux.intel.com>
---
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