[RFC PATCH 1/5] bug: Core support for suppressing warning backtraces

From: Guenter Roeck
Date: Tue Mar 05 2024 - 13:41:06 EST

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Some unit tests intentionally trigger warning backtraces by passing
bad parameters to API functions. Such unit tests typically check the
return value from those calls, not the existence of the warning backtrace.

Such intentionally generated warning backtraces are neither desirable
nor useful for a number of reasons.
- They can result in overlooked real problems.
- A warning that suddenly starts to show up in unit tests needs to be
investigated and has to be marked to be ignored, for example by
adjusting filter scripts. Such filters are ad-hoc because there is
no real standard format for warnings. On top of that, such filter
scripts would require constant maintenance.

One option to address problem would be to add messages such as "expected
warning backtraces start / end here" to the kernel log. However, that
would again require filter scripts, it might result in missing real
problematic warning backtraces triggered while the test is running, and
the irrelevant backtrace(s) would still clog the kernel log.

Solve the problem by providing a means to identify and suppress specific
warning backtraces while executing test code.

Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: Daniel Diaz <daniel.diaz@xxxxxxxxxx>
Cc: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
include/asm-generic/bug.h | 16 +++++++++---
include/kunit/bug.h | 51 +++++++++++++++++++++++++++++++++++++++
include/linux/bug.h | 13 ++++++++++
lib/bug.c | 51 ++++++++++++++++++++++++++++++++++++---
lib/kunit/Makefile | 6 +++--
lib/kunit/bug.c | 40 ++++++++++++++++++++++++++++++
6 files changed, 168 insertions(+), 9 deletions(-)
create mode 100644 include/kunit/bug.h
create mode 100644 lib/kunit/bug.c

diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 6e794420bd39..b0069564eb8f 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -2,6 +2,7 @@
#ifndef _ASM_GENERIC_BUG_H
#define _ASM_GENERIC_BUG_H

+#include <kunit/bug.h>
#include <linux/compiler.h>
#include <linux/instrumentation.h>
#include <linux/once_lite.h>
@@ -39,8 +40,14 @@ struct bug_entry {
#ifdef CONFIG_DEBUG_BUGVERBOSE
#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
const char *file;
+#ifdef HAVE_BUG_FUNCTION
+ const char *function;
+#endif
#else
signed int file_disp;
+#ifdef HAVE_BUG_FUNCTION
+ signed int function_disp;
+#endif
#endif
unsigned short line;
#endif
@@ -96,15 +103,18 @@ extern __printf(1, 2) void __warn_printk(const char *fmt, ...);
#define __WARN() __WARN_printf(TAINT_WARN, NULL)
#define __WARN_printf(taint, arg...) do { \
instrumentation_begin(); \
- warn_slowpath_fmt(__FILE__, __LINE__, taint, arg); \
+ if (!IS_SUPPRESSED_WARNING(__func__)) \
+ warn_slowpath_fmt(__FILE__, __LINE__, taint, arg);\
instrumentation_end(); \
} while (0)
#else
#define __WARN() __WARN_FLAGS(BUGFLAG_TAINT(TAINT_WARN))
#define __WARN_printf(taint, arg...) do { \
instrumentation_begin(); \
- __warn_printk(arg); \
- __WARN_FLAGS(BUGFLAG_NO_CUT_HERE | BUGFLAG_TAINT(taint));\
+ if (!IS_SUPPRESSED_WARNING(__func__)) { \
+ __warn_printk(arg); \
+ __WARN_FLAGS(BUGFLAG_NO_CUT_HERE | BUGFLAG_TAINT(taint));\
+ } \
instrumentation_end(); \
} while (0)
#define WARN_ON_ONCE(condition) ({ \
diff --git a/include/kunit/bug.h b/include/kunit/bug.h
new file mode 100644
index 000000000000..11b8ae795320
--- /dev/null
+++ b/include/kunit/bug.h
@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * KUnit helpers for backtrace suppression
+ *
+ * Copyright (c) 2024 Guenter Roeck <linux@xxxxxxxxxxxx>
+ */
+
+#ifndef _KUNIT_BUG_H
+#define _KUNIT_BUG_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/kconfig.h>
+
+#if IS_ENABLED(CONFIG_KUNIT)
+
+#include <linux/types.h>
+#include <linux/stringify.h>
+
+struct __suppressed_warning {
+ struct list_head node;
+ const char *function;
+};
+
+void __start_suppress_warning(struct __suppressed_warning *warning);
+void __end_suppress_warning(struct __suppressed_warning *warning);
+bool __is_suppressed_warning(const char *function);
+
+#define DEFINE_SUPPRESSED_WARNING(func) \
+ struct __suppressed_warning __kunit_suppress_##func = \
+ { .function = __stringify(func) }
+
+#define START_SUPPRESSED_WARNING(func) \
+ __start_suppress_warning(&__kunit_suppress_##func)
+
+#define END_SUPPRESSED_WARNING(func) \
+ __end_suppress_warning(&__kunit_suppress_##func)
+
+#define IS_SUPPRESSED_WARNING(func) \
+ __is_suppressed_warning(func)
+
+#else /* CONFIG_KUNIT */
+
+#define DEFINE_SUPPRESSED_WARNING(func)
+#define START_SUPPRESSED_WARNING(func)
+#define END_SUPPRESSED_WARNING(func)
+#define IS_SUPPRESSED_WARNING(func) (false)
+
+#endif /* CONFIG_KUNIT */
+#endif /* __ASSEMBLY__ */
+#endif /* _KUNIT_BUG_H */
diff --git a/include/linux/bug.h b/include/linux/bug.h
index 348acf2558f3..c668762dc76a 100644
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -36,6 +36,9 @@ static inline int is_warning_bug(const struct bug_entry *bug)
return bug->flags & BUGFLAG_WARNING;
}

+void bug_get_file_function_line(struct bug_entry *bug, const char **file,
+ const char **function, unsigned int *line);
+
void bug_get_file_line(struct bug_entry *bug, const char **file,
unsigned int *line);

@@ -62,6 +65,16 @@ static inline enum bug_trap_type report_bug(unsigned long bug_addr,
}

struct bug_entry;
+static inline void bug_get_file_function_line(struct bug_entry *bug,
+ const char **file,
+ const char **function,
+ unsigned int *line)
+{
+ *file = NULL;
+ *function = NULL;
+ *line = 0;
+}
+
static inline void bug_get_file_line(struct bug_entry *bug, const char **file,
unsigned int *line)
{
diff --git a/lib/bug.c b/lib/bug.c
index e0ff21989990..6b85d4042e07 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -26,6 +26,14 @@
when CONFIG_DEBUG_BUGVERBOSE is not enabled, so you must generate
the values accordingly.

+ 2a.Optionally implement support for the "function" entry in struct
+ bug_entry. This entry must point to the name of the function triggering
+ the warning or bug trap (normally __func__). This is only needed if
+ both CONFIG_DEBUG_BUGVERBOSE and CONFIG_KUNIT are enabled and if
+ the architecture wants to implement support for suppressing warning
+ backtraces. The architecture must define HAVE_BUG_FUNCTION if it adds
+ pointers to function names to struct bug_entry.
+
3. Implement the trap
- In the illegal instruction trap handler (typically), verify
that the fault was in kernel mode, and call report_bug()
@@ -127,14 +135,21 @@ static inline struct bug_entry *module_find_bug(unsigned long bugaddr)
}
#endif

-void bug_get_file_line(struct bug_entry *bug, const char **file,
- unsigned int *line)
+void bug_get_file_function_line(struct bug_entry *bug, const char **file,
+ const char **function, unsigned int *line)
{
+ *function = NULL;
#ifdef CONFIG_DEBUG_BUGVERBOSE
#ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
*file = (const char *)&bug->file_disp + bug->file_disp;
+#ifdef HAVE_BUG_FUNCTION
+ *function = (const char *)&bug->function_disp + bug->function_disp;
+#endif
#else
*file = bug->file;
+#ifdef HAVE_BUG_FUNCTION
+ *function = bug->function;
+#endif
#endif
*line = bug->line;
#else
@@ -143,6 +158,13 @@ void bug_get_file_line(struct bug_entry *bug, const char **file,
#endif
}

+void bug_get_file_line(struct bug_entry *bug, const char **file, unsigned int *line)
+{
+ const char *function;
+
+ bug_get_file_function_line(bug, file, &function, line);
+}
+
struct bug_entry *find_bug(unsigned long bugaddr)
{
struct bug_entry *bug;
@@ -157,8 +179,9 @@ struct bug_entry *find_bug(unsigned long bugaddr)
static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *regs)
{
struct bug_entry *bug;
- const char *file;
+ const char *file, *function;
unsigned line, warning, once, done;
+ char __maybe_unused sym[KSYM_SYMBOL_LEN];

if (!is_valid_bugaddr(bugaddr))
return BUG_TRAP_TYPE_NONE;
@@ -169,12 +192,32 @@ static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *re

disable_trace_on_warning();

- bug_get_file_line(bug, &file, &line);
+ bug_get_file_function_line(bug, &file, &function, &line);
+#if IS_ENABLED(CONFIG_KUNIT) && defined(CONFIG_KALLSYMS)
+ if (!function) {
+ /*
+ * This will be seen if report_bug is called on an architecture
+ * with no architecture-specific support for suppressing warning
+ * backtraces, if CONFIG_DEBUG_BUGVERBOSE is not enabled, or if
+ * the calling code is from assembler which does not record a
+ * function name. Extracting the function name from the bug
+ * address is less than perfect since compiler optimization may
+ * result in 'bugaddr' pointing to a function which does not
+ * actually trigger the warning, but it is better than no
+ * suppression at all.
+ */
+ sprint_symbol_no_offset(sym, bugaddr);
+ function = sym;
+ }
+#endif /* IS_ENABLED(CONFIG_KUNIT) && defined(CONFIG_KALLSYMS) */

warning = (bug->flags & BUGFLAG_WARNING) != 0;
once = (bug->flags & BUGFLAG_ONCE) != 0;
done = (bug->flags & BUGFLAG_DONE) != 0;

+ if (warning && IS_SUPPRESSED_WARNING(function))
+ return BUG_TRAP_TYPE_WARN;
+
if (warning && once) {
if (done)
return BUG_TRAP_TYPE_WARN;
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index 309659a32a78..545b57c3be48 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -14,8 +14,10 @@ ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
kunit-objs += debugfs.o
endif

-# KUnit 'hooks' are built-in even when KUnit is built as a module.
-obj-y += hooks.o
+# KUnit 'hooks' and bug handling are built-in even when KUnit is built
+# as a module.
+obj-y += hooks.o \
+ bug.o

obj-$(CONFIG_KUNIT_TEST) += kunit-test.o

diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
new file mode 100644
index 000000000000..f93544d7a9d1
--- /dev/null
+++ b/lib/kunit/bug.c
@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit helpers for backtrace suppression
+ *
+ * Copyright (c) 2024 Guenter Roeck <linux@xxxxxxxxxxxx>
+ */
+
+#include <kunit/bug.h>
+#include <linux/export.h>
+#include <linux/list.h>
+#include <linux/string.h>
+
+static LIST_HEAD(suppressed_warnings);
+
+void __start_suppress_warning(struct __suppressed_warning *warning)
+{
+ list_add(&warning->node, &suppressed_warnings);
+}
+EXPORT_SYMBOL_GPL(__start_suppress_warning);
+
+void __end_suppress_warning(struct __suppressed_warning *warning)
+{
+ list_del(&warning->node);
+}
+EXPORT_SYMBOL_GPL(__end_suppress_warning);
+
+bool __is_suppressed_warning(const char *function)
+{
+ struct __suppressed_warning *warning;
+
+ if (!function)
+ return false;
+
+ list_for_each_entry(warning, &suppressed_warnings, node) {
+ if (!strcmp(function, warning->function))
+ return true;
+ }
+ return false;
+}
+EXPORT_SYMBOL_GPL(__is_suppressed_warning);
--
2.39.2

Next message: Guenter Roeck: "[RFC PATCH 2/5] drm: Suppress intentional warning backtraces in scaling unit tests"
Previous message: Guenter Roeck: "[RFC PATCH 0/5] Add support for suppressing warning backtraces"
In reply to: Guenter Roeck: "[RFC PATCH 0/5] Add support for suppressing warning backtraces"
Next in thread: Kees Cook: "Re: [RFC PATCH 1/5] bug: Core support for suppressing warning backtraces"
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