* [PATCH v7 1/5] bug/kunit: Core support for suppressing warning backtraces
2026-04-20 12:28 [PATCH v7 0/5] kunit: Add support for suppressing warning backtraces Albert Esteve
@ 2026-04-20 12:28 ` Albert Esteve
2026-04-20 14:39 ` Peter Zijlstra
` (2 more replies)
2026-04-20 12:28 ` [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression Albert Esteve
` (3 subsequent siblings)
4 siblings, 3 replies; 20+ messages in thread
From: Albert Esteve @ 2026-04-20 12:28 UTC (permalink / raw)
To: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Alessandro Carminati, Guenter Roeck,
Kees Cook, Albert Esteve
From: Alessandro Carminati <acarmina@redhat.com>
Some unit tests intentionally trigger warning backtraces by passing bad
parameters to kernel API functions. Such unit tests typically check the
return value from such 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.
Solve the problem by providing a means to identify and suppress specific
warning backtraces while executing test code. Support suppressing multiple
backtraces while at the same time limiting changes to generic code to the
absolute minimum.
Implementation details:
Suppression is checked at two points in the warning path:
- In warn_slowpath_fmt(), the check runs before any output, fully
suppressing both message and backtrace.
- In __report_bug(), the check runs before __warn() is called,
suppressing the backtrace and stack dump. Note that on this path,
the WARN() format message may still appear in the kernel log since
__warn_printk() runs before the trap that enters __report_bug().
A helper function, `__kunit_is_suppressed_warning()`, walks an
RCU-protected list of active suppressions, matching by current task.
The suppression state is tied to the KUnit test lifecycle via
kunit_add_action(), ensuring automatic cleanup at test exit.
The list of suppressed warnings is protected with RCU to allow
concurrent read access without locks.
The implementation is deliberately simple and avoids architecture-specific
optimizations to preserve portability.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
include/kunit/bug.h | 56 +++++++++++++++++++++++++++++++++++
include/kunit/test.h | 1 +
kernel/panic.c | 8 ++++-
lib/bug.c | 8 +++++
lib/kunit/Kconfig | 9 ++++++
lib/kunit/Makefile | 6 ++--
lib/kunit/bug.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++
7 files changed, 169 insertions(+), 3 deletions(-)
diff --git a/include/kunit/bug.h b/include/kunit/bug.h
new file mode 100644
index 0000000000000..e52c9d21d9fe6
--- /dev/null
+++ b/include/kunit/bug.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * KUnit helpers for backtrace suppression
+ *
+ * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
+ * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
+ */
+
+#ifndef _KUNIT_BUG_H
+#define _KUNIT_BUG_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/kconfig.h>
+
+struct kunit;
+
+#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
+
+#include <linux/types.h>
+
+struct task_struct;
+
+struct __suppressed_warning {
+ struct list_head node;
+ struct task_struct *task;
+ int counter;
+};
+
+struct __suppressed_warning *
+__kunit_start_suppress_warning(struct kunit *test);
+void __kunit_end_suppress_warning(struct kunit *test,
+ struct __suppressed_warning *warning);
+int __kunit_suppressed_warning_count(struct __suppressed_warning *warning);
+bool __kunit_is_suppressed_warning(void);
+
+#define KUNIT_START_SUPPRESSED_WARNING(test) \
+ struct __suppressed_warning *__kunit_suppress = \
+ __kunit_start_suppress_warning(test)
+
+#define KUNIT_END_SUPPRESSED_WARNING(test) \
+ __kunit_end_suppress_warning(test, __kunit_suppress)
+
+#define KUNIT_SUPPRESSED_WARNING_COUNT() \
+ __kunit_suppressed_warning_count(__kunit_suppress)
+
+#else /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
+
+#define KUNIT_START_SUPPRESSED_WARNING(test)
+#define KUNIT_END_SUPPRESSED_WARNING(test)
+#define KUNIT_SUPPRESSED_WARNING_COUNT() 0
+static inline bool __kunit_is_suppressed_warning(void) { return false; }
+
+#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
+#endif /* __ASSEMBLY__ */
+#endif /* _KUNIT_BUG_H */
diff --git a/include/kunit/test.h b/include/kunit/test.h
index 9cd1594ab697d..4ec07b3fa0204 100644
--- a/include/kunit/test.h
+++ b/include/kunit/test.h
@@ -10,6 +10,7 @@
#define _KUNIT_TEST_H
#include <kunit/assert.h>
+#include <kunit/bug.h>
#include <kunit/try-catch.h>
#include <linux/args.h>
diff --git a/kernel/panic.c b/kernel/panic.c
index c78600212b6c1..d7a7a679f56c4 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -39,6 +39,7 @@
#include <linux/sys_info.h>
#include <trace/events/error_report.h>
#include <asm/sections.h>
+#include <kunit/bug.h>
#define PANIC_TIMER_STEP 100
#define PANIC_BLINK_SPD 18
@@ -1080,9 +1081,14 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
void warn_slowpath_fmt(const char *file, int line, unsigned taint,
const char *fmt, ...)
{
- bool rcu = warn_rcu_enter();
+ bool rcu;
struct warn_args args;
+ if (__kunit_is_suppressed_warning())
+ return;
+
+ rcu = warn_rcu_enter();
+
pr_warn(CUT_HERE);
if (!fmt) {
diff --git a/lib/bug.c b/lib/bug.c
index 623c467a8b76c..606205c8c302f 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -48,6 +48,7 @@
#include <linux/rculist.h>
#include <linux/ftrace.h>
#include <linux/context_tracking.h>
+#include <kunit/bug.h>
extern struct bug_entry __start___bug_table[], __stop___bug_table[];
@@ -223,6 +224,13 @@ static enum bug_trap_type __report_bug(struct bug_entry *bug, unsigned long buga
no_cut = bug->flags & BUGFLAG_NO_CUT_HERE;
has_args = bug->flags & BUGFLAG_ARGS;
+ /*
+ * Before the once logic so suppressed warnings do not consume
+ * the single-fire budget of WARN_ON_ONCE().
+ */
+ if (warning && __kunit_is_suppressed_warning())
+ return BUG_TRAP_TYPE_WARN;
+
if (warning && once) {
if (done)
return BUG_TRAP_TYPE_WARN;
diff --git a/lib/kunit/Kconfig b/lib/kunit/Kconfig
index 498cc51e493dc..57527418fcf09 100644
--- a/lib/kunit/Kconfig
+++ b/lib/kunit/Kconfig
@@ -15,6 +15,15 @@ menuconfig KUNIT
if KUNIT
+config KUNIT_SUPPRESS_BACKTRACE
+ bool "KUnit - Enable backtrace suppression"
+ default y
+ help
+ Enable backtrace suppression for KUnit. If enabled, backtraces
+ generated intentionally by KUnit tests are suppressed. Disable
+ to reduce kernel image size if image size is more important than
+ suppression of backtraces generated by KUnit tests.
+
config KUNIT_DEBUGFS
bool "KUnit - Enable /sys/kernel/debug/kunit debugfs representation" if !KUNIT_ALL_TESTS
default KUNIT_ALL_TESTS
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index 656f1fa35abcc..fe177ff3ebdef 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -16,8 +16,10 @@ ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
kunit-objs += debugfs.o
endif
-# KUnit 'hooks' are built-in even when KUnit is built as a module.
-obj-$(if $(CONFIG_KUNIT),y) += hooks.o
+# KUnit 'hooks' and bug handling are built-in even when KUnit is built
+# as a module.
+obj-$(if $(CONFIG_KUNIT),y) += hooks.o \
+ bug.o
obj-$(CONFIG_KUNIT_TEST) += kunit-test.o
obj-$(CONFIG_KUNIT_TEST) += platform-test.o
diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
new file mode 100644
index 0000000000000..356c8a5928828
--- /dev/null
+++ b/lib/kunit/bug.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit helpers for backtrace suppression
+ *
+ * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
+ * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
+ */
+
+#include <kunit/bug.h>
+#include <kunit/resource.h>
+#include <linux/export.h>
+#include <linux/rculist.h>
+#include <linux/sched.h>
+
+#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
+
+static LIST_HEAD(suppressed_warnings);
+
+static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
+{
+ list_del_rcu(&warning->node);
+ synchronize_rcu(); /* Wait for readers to finish */
+}
+
+KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
+ __kunit_suppress_warning_remove,
+ struct __suppressed_warning *);
+
+struct __suppressed_warning *
+__kunit_start_suppress_warning(struct kunit *test)
+{
+ struct __suppressed_warning *warning;
+ int ret;
+
+ warning = kunit_kzalloc(test, sizeof(*warning), GFP_KERNEL);
+ if (!warning)
+ return NULL;
+
+ warning->task = current;
+ list_add_rcu(&warning->node, &suppressed_warnings);
+
+ ret = kunit_add_action_or_reset(test,
+ __kunit_suppress_warning_cleanup,
+ warning);
+ if (ret)
+ return NULL;
+
+ return warning;
+}
+EXPORT_SYMBOL_GPL(__kunit_start_suppress_warning);
+
+void __kunit_end_suppress_warning(struct kunit *test,
+ struct __suppressed_warning *warning)
+{
+ if (!warning)
+ return;
+ kunit_release_action(test, __kunit_suppress_warning_cleanup, warning);
+}
+EXPORT_SYMBOL_GPL(__kunit_end_suppress_warning);
+
+int __kunit_suppressed_warning_count(struct __suppressed_warning *warning)
+{
+ return warning ? warning->counter : 0;
+}
+EXPORT_SYMBOL_GPL(__kunit_suppressed_warning_count);
+
+bool __kunit_is_suppressed_warning(void)
+{
+ struct __suppressed_warning *warning;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
+ if (warning->task == current) {
+ warning->counter++;
+ rcu_read_unlock();
+ return true;
+ }
+ }
+ rcu_read_unlock();
+
+ return false;
+}
+
+#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread* Re: [PATCH v7 1/5] bug/kunit: Core support for suppressing warning backtraces
2026-04-20 12:28 ` [PATCH v7 1/5] bug/kunit: Core " Albert Esteve
@ 2026-04-20 14:39 ` Peter Zijlstra
2026-04-21 8:22 ` Albert Esteve
2026-04-20 14:45 ` Peter Zijlstra
2026-04-22 12:19 ` David Gow
2 siblings, 1 reply; 20+ messages in thread
From: Peter Zijlstra @ 2026-04-20 14:39 UTC (permalink / raw)
To: Albert Esteve
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati, Guenter Roeck,
Kees Cook
On Mon, Apr 20, 2026 at 02:28:03PM +0200, Albert Esteve wrote:
> From: Alessandro Carminati <acarmina@redhat.com>
>
> Some unit tests intentionally trigger warning backtraces by passing bad
> parameters to kernel API functions. Such unit tests typically check the
> return value from such 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.
>
> Solve the problem by providing a means to identify and suppress specific
> warning backtraces while executing test code. Support suppressing multiple
> backtraces while at the same time limiting changes to generic code to the
> absolute minimum.
>
> Implementation details:
> Suppression is checked at two points in the warning path:
> - In warn_slowpath_fmt(), the check runs before any output, fully
> suppressing both message and backtrace.
> - In __report_bug(), the check runs before __warn() is called,
> suppressing the backtrace and stack dump. Note that on this path,
> the WARN() format message may still appear in the kernel log since
> __warn_printk() runs before the trap that enters __report_bug().
This is for architectures that implement __WARN_FLAGS but not
__WARN_printf right? (which is arm64, loongarch, parisc, powerpc, riscv,
sh, afaict). ARM64 should eventually get __WARN_printf, but other than
that this should be fixable by moving __WARN_FLAGS() into
__warn_printk() or so. This is the only __warn_printk() user anyway.
> diff --git a/include/kunit/bug.h b/include/kunit/bug.h
> new file mode 100644
> index 0000000000000..e52c9d21d9fe6
> --- /dev/null
> +++ b/include/kunit/bug.h
> @@ -0,0 +1,56 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * KUnit helpers for backtrace suppression
> + *
> + * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
> + * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
> + */
> +
> +#ifndef _KUNIT_BUG_H
> +#define _KUNIT_BUG_H
> +
> +#ifndef __ASSEMBLY__
> +
> +#include <linux/kconfig.h>
> +
> +struct kunit;
> +
> +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> +
> +#include <linux/types.h>
> +
> +struct task_struct;
> +
> +struct __suppressed_warning {
> + struct list_head node;
> + struct task_struct *task;
> + int counter;
> +};
> +
> +struct __suppressed_warning *
> +__kunit_start_suppress_warning(struct kunit *test);
> +void __kunit_end_suppress_warning(struct kunit *test,
> + struct __suppressed_warning *warning);
> +int __kunit_suppressed_warning_count(struct __suppressed_warning *warning);
> +bool __kunit_is_suppressed_warning(void);
> +
> +#define KUNIT_START_SUPPRESSED_WARNING(test) \
> + struct __suppressed_warning *__kunit_suppress = \
> + __kunit_start_suppress_warning(test)
> +
> +#define KUNIT_END_SUPPRESSED_WARNING(test) \
> + __kunit_end_suppress_warning(test, __kunit_suppress)
We have __cleanup for this?
> +
> +#define KUNIT_SUPPRESSED_WARNING_COUNT() \
> + __kunit_suppressed_warning_count(__kunit_suppress)
> +
> +#else /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> +
> +#define KUNIT_START_SUPPRESSED_WARNING(test)
> +#define KUNIT_END_SUPPRESSED_WARNING(test)
> +#define KUNIT_SUPPRESSED_WARNING_COUNT() 0
> +static inline bool __kunit_is_suppressed_warning(void) { return false; }
> +
> +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> +#endif /* __ASSEMBLY__ */
> +#endif /* _KUNIT_BUG_H */
> diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
> index 656f1fa35abcc..fe177ff3ebdef 100644
> --- a/lib/kunit/Makefile
> +++ b/lib/kunit/Makefile
> @@ -16,8 +16,10 @@ ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
> kunit-objs += debugfs.o
> endif
>
> -# KUnit 'hooks' are built-in even when KUnit is built as a module.
> -obj-$(if $(CONFIG_KUNIT),y) += hooks.o
> +# KUnit 'hooks' and bug handling are built-in even when KUnit is built
> +# as a module.
> +obj-$(if $(CONFIG_KUNIT),y) += hooks.o \
> + bug.o
>
> obj-$(CONFIG_KUNIT_TEST) += kunit-test.o
> obj-$(CONFIG_KUNIT_TEST) += platform-test.o
> diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
> new file mode 100644
> index 0000000000000..356c8a5928828
> --- /dev/null
> +++ b/lib/kunit/bug.c
> @@ -0,0 +1,84 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KUnit helpers for backtrace suppression
> + *
> + * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
> + * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
> + */
> +
> +#include <kunit/bug.h>
> +#include <kunit/resource.h>
> +#include <linux/export.h>
> +#include <linux/rculist.h>
> +#include <linux/sched.h>
> +
> +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> +
> +static LIST_HEAD(suppressed_warnings);
> +
> +static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
> +{
> + list_del_rcu(&warning->node);
> + synchronize_rcu(); /* Wait for readers to finish */
> +}
> +
> +KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
> + __kunit_suppress_warning_remove,
> + struct __suppressed_warning *);
> +
> +struct __suppressed_warning *
> +__kunit_start_suppress_warning(struct kunit *test)
> +{
> + struct __suppressed_warning *warning;
> + int ret;
> +
> + warning = kunit_kzalloc(test, sizeof(*warning), GFP_KERNEL);
> + if (!warning)
> + return NULL;
> +
> + warning->task = current;
> + list_add_rcu(&warning->node, &suppressed_warnings);
What if anything serializes this global list?
> +
> + ret = kunit_add_action_or_reset(test,
> + __kunit_suppress_warning_cleanup,
> + warning);
> + if (ret)
> + return NULL;
> +
> + return warning;
> +}
> +EXPORT_SYMBOL_GPL(__kunit_start_suppress_warning);
> +
> +void __kunit_end_suppress_warning(struct kunit *test,
> + struct __suppressed_warning *warning)
> +{
> + if (!warning)
> + return;
> + kunit_release_action(test, __kunit_suppress_warning_cleanup, warning);
> +}
> +EXPORT_SYMBOL_GPL(__kunit_end_suppress_warning);
> +
> +int __kunit_suppressed_warning_count(struct __suppressed_warning *warning)
> +{
> + return warning ? warning->counter : 0;
> +}
> +EXPORT_SYMBOL_GPL(__kunit_suppressed_warning_count);
> +
> +bool __kunit_is_suppressed_warning(void)
> +{
> + struct __suppressed_warning *warning;
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> + if (warning->task == current) {
> + warning->counter++;
> + rcu_read_unlock();
> + return true;
> + }
> + }
> + rcu_read_unlock();
> +
> + return false;
> +}
> +
> +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
>
> --
> 2.52.0
>
^ permalink raw reply [flat|nested] 20+ messages in thread* Re: [PATCH v7 1/5] bug/kunit: Core support for suppressing warning backtraces
2026-04-20 14:39 ` Peter Zijlstra
@ 2026-04-21 8:22 ` Albert Esteve
0 siblings, 0 replies; 20+ messages in thread
From: Albert Esteve @ 2026-04-21 8:22 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati, Guenter Roeck,
Kees Cook
On Mon, Apr 20, 2026 at 4:40 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Apr 20, 2026 at 02:28:03PM +0200, Albert Esteve wrote:
> > From: Alessandro Carminati <acarmina@redhat.com>
> >
> > Some unit tests intentionally trigger warning backtraces by passing bad
> > parameters to kernel API functions. Such unit tests typically check the
> > return value from such 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.
> >
> > Solve the problem by providing a means to identify and suppress specific
> > warning backtraces while executing test code. Support suppressing multiple
> > backtraces while at the same time limiting changes to generic code to the
> > absolute minimum.
> >
> > Implementation details:
> > Suppression is checked at two points in the warning path:
> > - In warn_slowpath_fmt(), the check runs before any output, fully
> > suppressing both message and backtrace.
> > - In __report_bug(), the check runs before __warn() is called,
> > suppressing the backtrace and stack dump. Note that on this path,
> > the WARN() format message may still appear in the kernel log since
> > __warn_printk() runs before the trap that enters __report_bug().
>
> This is for architectures that implement __WARN_FLAGS but not
> __WARN_printf right? (which is arm64, loongarch, parisc, powerpc, riscv,
> sh, afaict). ARM64 should eventually get __WARN_printf, but other than
> that this should be fixable by moving __WARN_FLAGS() into
> __warn_printk() or so. This is the only __warn_printk() user anyway.
Right. On that path, __warn_printk() prints the message before
__WARN_FLAGS() triggers the trap into __report_bug(), so the
suppression check in __report_bug() only catches the backtrace.
Adding the suppression check to __warn_printk() as well should close
this gap, since it's the only caller in the generic __WARN_printf
path. Something like:
```
diff --git a/kernel/panic.c b/kernel/panic.c
index d7a7a679f56c4..cd73038b7c0bd 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -1108,9 +1108,14 @@ EXPORT_SYMBOL(warn_slowpath_fmt);
#else
void __warn_printk(const char *fmt, ...)
{
- bool rcu = warn_rcu_enter();
+ bool rcu;
va_list args;
+ if (__kunit_is_suppressed_warning())
+ return;
+
+ rcu = warn_rcu_enter();
+
pr_warn(CUT_HERE);
va_start(args, fmt);
```
Note that the suppression counter tracking may need a small adjustment
to avoid double-counting, since __report_bug() will still see the same
warning through the trap path, but the approach itself should be
straightforward.
>
>
> > diff --git a/include/kunit/bug.h b/include/kunit/bug.h
> > new file mode 100644
> > index 0000000000000..e52c9d21d9fe6
> > --- /dev/null
> > +++ b/include/kunit/bug.h
> > @@ -0,0 +1,56 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * KUnit helpers for backtrace suppression
> > + *
> > + * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
> > + * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
> > + */
> > +
> > +#ifndef _KUNIT_BUG_H
> > +#define _KUNIT_BUG_H
> > +
> > +#ifndef __ASSEMBLY__
> > +
> > +#include <linux/kconfig.h>
> > +
> > +struct kunit;
> > +
> > +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> > +
> > +#include <linux/types.h>
> > +
> > +struct task_struct;
> > +
> > +struct __suppressed_warning {
> > + struct list_head node;
> > + struct task_struct *task;
> > + int counter;
> > +};
> > +
> > +struct __suppressed_warning *
> > +__kunit_start_suppress_warning(struct kunit *test);
> > +void __kunit_end_suppress_warning(struct kunit *test,
> > + struct __suppressed_warning *warning);
> > +int __kunit_suppressed_warning_count(struct __suppressed_warning *warning);
> > +bool __kunit_is_suppressed_warning(void);
> > +
> > +#define KUNIT_START_SUPPRESSED_WARNING(test) \
> > + struct __suppressed_warning *__kunit_suppress = \
> > + __kunit_start_suppress_warning(test)
> > +
> > +#define KUNIT_END_SUPPRESSED_WARNING(test) \
> > + __kunit_end_suppress_warning(test, __kunit_suppress)
>
> We have __cleanup for this?
I was unfamiliar with this attribute. I have looked into it a bit, and
it could be a good fit. I saw a good example in seqlock. I could try
to use it for the next version.
>
> > +
> > +#define KUNIT_SUPPRESSED_WARNING_COUNT() \
> > + __kunit_suppressed_warning_count(__kunit_suppress)
> > +
> > +#else /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> > +
> > +#define KUNIT_START_SUPPRESSED_WARNING(test)
> > +#define KUNIT_END_SUPPRESSED_WARNING(test)
> > +#define KUNIT_SUPPRESSED_WARNING_COUNT() 0
> > +static inline bool __kunit_is_suppressed_warning(void) { return false; }
> > +
> > +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> > +#endif /* __ASSEMBLY__ */
> > +#endif /* _KUNIT_BUG_H */
>
> > diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
> > index 656f1fa35abcc..fe177ff3ebdef 100644
> > --- a/lib/kunit/Makefile
> > +++ b/lib/kunit/Makefile
> > @@ -16,8 +16,10 @@ ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
> > kunit-objs += debugfs.o
> > endif
> >
> > -# KUnit 'hooks' are built-in even when KUnit is built as a module.
> > -obj-$(if $(CONFIG_KUNIT),y) += hooks.o
> > +# KUnit 'hooks' and bug handling are built-in even when KUnit is built
> > +# as a module.
> > +obj-$(if $(CONFIG_KUNIT),y) += hooks.o \
> > + bug.o
> >
> > obj-$(CONFIG_KUNIT_TEST) += kunit-test.o
> > obj-$(CONFIG_KUNIT_TEST) += platform-test.o
> > diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
> > new file mode 100644
> > index 0000000000000..356c8a5928828
> > --- /dev/null
> > +++ b/lib/kunit/bug.c
> > @@ -0,0 +1,84 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * KUnit helpers for backtrace suppression
> > + *
> > + * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
> > + * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
> > + */
> > +
> > +#include <kunit/bug.h>
> > +#include <kunit/resource.h>
> > +#include <linux/export.h>
> > +#include <linux/rculist.h>
> > +#include <linux/sched.h>
> > +
> > +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> > +
> > +static LIST_HEAD(suppressed_warnings);
> > +
> > +static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
> > +{
> > + list_del_rcu(&warning->node);
> > + synchronize_rcu(); /* Wait for readers to finish */
> > +}
> > +
> > +KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
> > + __kunit_suppress_warning_remove,
> > + struct __suppressed_warning *);
> > +
> > +struct __suppressed_warning *
> > +__kunit_start_suppress_warning(struct kunit *test)
> > +{
> > + struct __suppressed_warning *warning;
> > + int ret;
> > +
> > + warning = kunit_kzalloc(test, sizeof(*warning), GFP_KERNEL);
> > + if (!warning)
> > + return NULL;
> > +
> > + warning->task = current;
> > + list_add_rcu(&warning->node, &suppressed_warnings);
>
> What if anything serializes this global list?
I considered adding a spinlock, but since the KUnit executor runs
tests sequentially and it had not been a concern in previous versions,
I left it out to keep the changeset minimal unless someone complains.
If we want a hard guarantee, I'm happy to add the spinlock for the
next version.
>
> > +
> > + ret = kunit_add_action_or_reset(test,
> > + __kunit_suppress_warning_cleanup,
> > + warning);
> > + if (ret)
> > + return NULL;
> > +
> > + return warning;
> > +}
> > +EXPORT_SYMBOL_GPL(__kunit_start_suppress_warning);
> > +
> > +void __kunit_end_suppress_warning(struct kunit *test,
> > + struct __suppressed_warning *warning)
> > +{
> > + if (!warning)
> > + return;
> > + kunit_release_action(test, __kunit_suppress_warning_cleanup, warning);
> > +}
> > +EXPORT_SYMBOL_GPL(__kunit_end_suppress_warning);
> > +
> > +int __kunit_suppressed_warning_count(struct __suppressed_warning *warning)
> > +{
> > + return warning ? warning->counter : 0;
> > +}
> > +EXPORT_SYMBOL_GPL(__kunit_suppressed_warning_count);
> > +
> > +bool __kunit_is_suppressed_warning(void)
> > +{
> > + struct __suppressed_warning *warning;
> > +
> > + rcu_read_lock();
> > + list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> > + if (warning->task == current) {
> > + warning->counter++;
> > + rcu_read_unlock();
> > + return true;
> > + }
> > + }
> > + rcu_read_unlock();
> > +
> > + return false;
> > +}
> > +
> > +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> >
> > --
> > 2.52.0
> >
>
^ permalink raw reply related [flat|nested] 20+ messages in thread
* Re: [PATCH v7 1/5] bug/kunit: Core support for suppressing warning backtraces
2026-04-20 12:28 ` [PATCH v7 1/5] bug/kunit: Core " Albert Esteve
2026-04-20 14:39 ` Peter Zijlstra
@ 2026-04-20 14:45 ` Peter Zijlstra
2026-04-21 8:29 ` Albert Esteve
2026-04-22 12:19 ` David Gow
2 siblings, 1 reply; 20+ messages in thread
From: Peter Zijlstra @ 2026-04-20 14:45 UTC (permalink / raw)
To: Albert Esteve
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati, Guenter Roeck,
Kees Cook
On Mon, Apr 20, 2026 at 02:28:03PM +0200, Albert Esteve wrote:
> +bool __kunit_is_suppressed_warning(void)
> +{
> + struct __suppressed_warning *warning;
> +
> + rcu_read_lock();
guard(rcu)();
> + list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> + if (warning->task == current) {
> + warning->counter++;
> + rcu_read_unlock();
> + return true;
> + }
> + }
> + rcu_read_unlock();
> +
> + return false;
> +}
> +
> +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
>
> --
> 2.52.0
>
^ permalink raw reply [flat|nested] 20+ messages in thread* Re: [PATCH v7 1/5] bug/kunit: Core support for suppressing warning backtraces
2026-04-20 14:45 ` Peter Zijlstra
@ 2026-04-21 8:29 ` Albert Esteve
0 siblings, 0 replies; 20+ messages in thread
From: Albert Esteve @ 2026-04-21 8:29 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati, Guenter Roeck,
Kees Cook
On Mon, Apr 20, 2026 at 4:45 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Apr 20, 2026 at 02:28:03PM +0200, Albert Esteve wrote:
> > +bool __kunit_is_suppressed_warning(void)
> > +{
> > + struct __suppressed_warning *warning;
> > +
> > + rcu_read_lock();
>
> guard(rcu)();
Nice. I saw plenty of examples using explicit calls, but I had missed
the guard. Thanks for pointing it out.
>
> > + list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> > + if (warning->task == current) {
> > + warning->counter++;
> > + rcu_read_unlock();
> > + return true;
> > + }
> > + }
> > + rcu_read_unlock();
> > +
> > + return false;
> > +}
> > +
> > +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> >
> > --
> > 2.52.0
> >
>
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH v7 1/5] bug/kunit: Core support for suppressing warning backtraces
2026-04-20 12:28 ` [PATCH v7 1/5] bug/kunit: Core " Albert Esteve
2026-04-20 14:39 ` Peter Zijlstra
2026-04-20 14:45 ` Peter Zijlstra
@ 2026-04-22 12:19 ` David Gow
2 siblings, 0 replies; 20+ messages in thread
From: David Gow @ 2026-04-22 12:19 UTC (permalink / raw)
To: Albert Esteve, Arnd Bergmann, Brendan Higgins, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Alessandro Carminati, Guenter Roeck,
Kees Cook
Thanks very much for keeping this series alive! I'm very much in favour
of it, and I think the overall design is good. Lots of more detailed
nitpicks below, though.
Le 20/04/2026 à 8:28 PM, Albert Esteve a écrit :
> From: Alessandro Carminati <acarmina@redhat.com>
>
> Some unit tests intentionally trigger warning backtraces by passing bad
> parameters to kernel API functions. Such unit tests typically check the
> return value from such 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.
>
> Solve the problem by providing a means to identify and suppress specific
> warning backtraces while executing test code. Support suppressing multiple
> backtraces while at the same time limiting changes to generic code to the
> absolute minimum.
It sounds from the description here that suppressing "specific
backtraces" means that we're matching on the _contents_ of the stack
trace. This sort-of does that implicitly by checking they're in the same
kthread, but I think the fact that it's matching based on kthread should
be explicit in the commit message, like it is in the documentation.
>
> Implementation details:
> Suppression is checked at two points in the warning path:
> - In warn_slowpath_fmt(), the check runs before any output, fully
> suppressing both message and backtrace.
> - In __report_bug(), the check runs before __warn() is called,
> suppressing the backtrace and stack dump. Note that on this path,
> the WARN() format message may still appear in the kernel log since
> __warn_printk() runs before the trap that enters __report_bug().
Would it make sense to output a 'backtrace suppressed due to running
test' message in this latter case, so we don't just end up with the
WARN() format message by itself? (My gut feeling is 'no, it isn't worth
it', but it's food for thought.)
>
> A helper function, `__kunit_is_suppressed_warning()`, walks an
> RCU-protected list of active suppressions, matching by current task.
> The suppression state is tied to the KUnit test lifecycle via
> kunit_add_action(), ensuring automatic cleanup at test exit.
>
> The list of suppressed warnings is protected with RCU to allow
> concurrent read access without locks.
>
> The implementation is deliberately simple and avoids architecture-specific
> optimizations to preserve portability.
>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> Reviewed-by: Kees Cook <kees@kernel.org>
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
> include/kunit/bug.h | 56 +++++++++++++++++++++++++++++++++++
> include/kunit/test.h | 1 +
> kernel/panic.c | 8 ++++-
> lib/bug.c | 8 +++++
> lib/kunit/Kconfig | 9 ++++++
> lib/kunit/Makefile | 6 ++--
> lib/kunit/bug.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 7 files changed, 169 insertions(+), 3 deletions(-)
>
> diff --git a/include/kunit/bug.h b/include/kunit/bug.h
> new file mode 100644
> index 0000000000000..e52c9d21d9fe6
> --- /dev/null
> +++ b/include/kunit/bug.h
It's a bit confusing to name this bug.h when we have the (admittedly
terribly-named) test-bug.h header already. I'm pretty tempted to rename
the latter to something like 'hooks.h', as that's really what it's for,
and having a separate bug.h would be an incentive to do so, though, sit
it's not a big problem.
I do think that it'd be reasonable to include the backtrace suppression
tuff in the same file, though, if you'd rather. The
__kunit_is_suppressed_warning() stuff in particular fits the category of
"code called to change behaviour based on whether or not a test is
running", which is generally what the hooks are for. (And, if you'd
rather, there's a bunch of existing hooks and hook infrastructure you
could use.)
> @@ -0,0 +1,56 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * KUnit helpers for backtrace suppression
> + *
> + * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
> + * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
> + */
> +
> +#ifndef _KUNIT_BUG_H
> +#define _KUNIT_BUG_H
> +
> +#ifndef __ASSEMBLY__
> +
> +#include <linux/kconfig.h>
> +
> +struct kunit;
> +
> +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> +
> +#include <linux/types.h>
> +
> +struct task_struct;
> +
> +struct __suppressed_warning {
> + struct list_head node;
> + struct task_struct *task;
> + int counter;
> +};
> +
> +struct __suppressed_warning *
> +__kunit_start_suppress_warning(struct kunit *test);
> +void __kunit_end_suppress_warning(struct kunit *test,
> + struct __suppressed_warning *warning);
> +int __kunit_suppressed_warning_count(struct __suppressed_warning *warning);
> +bool __kunit_is_suppressed_warning(void);
> +
> +#define KUNIT_START_SUPPRESSED_WARNING(test) \
> + struct __suppressed_warning *__kunit_suppress = \
> + __kunit_start_suppress_warning(test)
> +
> +#define KUNIT_END_SUPPRESSED_WARNING(test) \
> + __kunit_end_suppress_warning(test, __kunit_suppress)
> +
> +#define KUNIT_SUPPRESSED_WARNING_COUNT() \
> + __kunit_suppressed_warning_count(__kunit_suppress)
Using a local variable (__kunit_suppress) here means that all of the
above macros must live in the same function. This is probably okay for
most use-cases, but more complicated tests may have to structure things
carefully. It also prevents there from being multiple START/END pairs in
the same function, and the KUNIT_SUPPRESSED_WARNING_COUNT() macro from
appearing before _START().
It also makes it less obvious that this cleans up nicely if the test
exits uncleanly, as the variable will have gone out-of-scope. (But given
we're just storing a pointer to heap-allocated memory, and
kunit_add_action() is used, it should be okay.)
One other option would be to allocate the suppression as a named
resource, which could then be retrieved from anywhere within the test
with kunit_find_named_resource(). (Though handling nested suppressions
gets a little more complicated here.)
Or you could make the struct __suppressed_warning pointer returned
explicitly user-visible, and let the user pass it around (though that
seems more work).
> +
> +#else /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> +
> +#define KUNIT_START_SUPPRESSED_WARNING(test)
> +#define KUNIT_END_SUPPRESSED_WARNING(test)
> +#define KUNIT_SUPPRESSED_WARNING_COUNT() 0
> +static inline bool __kunit_is_suppressed_warning(void) { return false; }
> +
> +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> +#endif /* __ASSEMBLY__ */
> +#endif /* _KUNIT_BUG_H */
> diff --git a/include/kunit/test.h b/include/kunit/test.h
> index 9cd1594ab697d..4ec07b3fa0204 100644
> --- a/include/kunit/test.h
> +++ b/include/kunit/test.h
> @@ -10,6 +10,7 @@
> #define _KUNIT_TEST_H
>
> #include <kunit/assert.h>
> +#include <kunit/bug.h>
> #include <kunit/try-catch.h>
>
> #include <linux/args.h>
> diff --git a/kernel/panic.c b/kernel/panic.c
> index c78600212b6c1..d7a7a679f56c4 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -39,6 +39,7 @@
> #include <linux/sys_info.h>
> #include <trace/events/error_report.h>
> #include <asm/sections.h>
> +#include <kunit/bug.h>
>
> #define PANIC_TIMER_STEP 100
> #define PANIC_BLINK_SPD 18
> @@ -1080,9 +1081,14 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
> void warn_slowpath_fmt(const char *file, int line, unsigned taint,
> const char *fmt, ...)
> {
> - bool rcu = warn_rcu_enter();
> + bool rcu;
> struct warn_args args;
>
> + if (__kunit_is_suppressed_warning())
> + return;
> +
> + rcu = warn_rcu_enter();
> +
> pr_warn(CUT_HERE);
>
> if (!fmt) {
> diff --git a/lib/bug.c b/lib/bug.c
> index 623c467a8b76c..606205c8c302f 100644
> --- a/lib/bug.c
> +++ b/lib/bug.c
> @@ -48,6 +48,7 @@
> #include <linux/rculist.h>
> #include <linux/ftrace.h>
> #include <linux/context_tracking.h>
> +#include <kunit/bug.h>
>
> extern struct bug_entry __start___bug_table[], __stop___bug_table[];
>
> @@ -223,6 +224,13 @@ static enum bug_trap_type __report_bug(struct bug_entry *bug, unsigned long buga
> no_cut = bug->flags & BUGFLAG_NO_CUT_HERE;
> has_args = bug->flags & BUGFLAG_ARGS;
>
> + /*
> + * Before the once logic so suppressed warnings do not consume
> + * the single-fire budget of WARN_ON_ONCE().
> + */
> + if (warning && __kunit_is_suppressed_warning())
> + return BUG_TRAP_TYPE_WARN;
> +
While any competant optimiser should get rid of this entirely, it might
be clearer to anyone reading it that this disappears if we just put it
behind an #ifdef?
> if (warning && once) {
> if (done)
> return BUG_TRAP_TYPE_WARN;
> diff --git a/lib/kunit/Kconfig b/lib/kunit/Kconfig
> index 498cc51e493dc..57527418fcf09 100644
> --- a/lib/kunit/Kconfig
> +++ b/lib/kunit/Kconfig
> @@ -15,6 +15,15 @@ menuconfig KUNIT
>
> if KUNIT
>
> +config KUNIT_SUPPRESS_BACKTRACE
> + bool "KUnit - Enable backtrace suppression"
> + default y
> + help
> + Enable backtrace suppression for KUnit. If enabled, backtraces
> + generated intentionally by KUnit tests are suppressed. Disable
> + to reduce kernel image size if image size is more important than
> + suppression of backtraces generated by KUnit tests.
> +
> config KUNIT_DEBUGFS
> bool "KUnit - Enable /sys/kernel/debug/kunit debugfs representation" if !KUNIT_ALL_TESTS
> default KUNIT_ALL_TESTS
> diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
> index 656f1fa35abcc..fe177ff3ebdef 100644
> --- a/lib/kunit/Makefile
> +++ b/lib/kunit/Makefile
> @@ -16,8 +16,10 @@ ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
> kunit-objs += debugfs.o
> endif
>
> -# KUnit 'hooks' are built-in even when KUnit is built as a module.
> -obj-$(if $(CONFIG_KUNIT),y) += hooks.o
> +# KUnit 'hooks' and bug handling are built-in even when KUnit is built
> +# as a module.
> +obj-$(if $(CONFIG_KUNIT),y) += hooks.o \
> + bug.o
Is there any reason we couldn't implement this on top of the hooks
mechanism? Then we could include the bug suppression code in the
kunit.ko module (albeit, with fewer possibilities for the compiler to
optimise things, as they'd have to go through an indirect pointer).
>
> obj-$(CONFIG_KUNIT_TEST) += kunit-test.o
> obj-$(CONFIG_KUNIT_TEST) += platform-test.o
> diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
> new file mode 100644
> index 0000000000000..356c8a5928828
> --- /dev/null
> +++ b/lib/kunit/bug.c
> @@ -0,0 +1,84 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KUnit helpers for backtrace suppression
> + *
> + * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
> + * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
> + */
> +
> +#include <kunit/bug.h>
> +#include <kunit/resource.h>
> +#include <linux/export.h>
> +#include <linux/rculist.h>
> +#include <linux/sched.h>
> +
> +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> +
> +static LIST_HEAD(suppressed_warnings);
> +
> +static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
> +{
> + list_del_rcu(&warning->node);
> + synchronize_rcu(); /* Wait for readers to finish */
> +}
> +
> +KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
> + __kunit_suppress_warning_remove,
> + struct __suppressed_warning *);
> +
> +struct __suppressed_warning *
> +__kunit_start_suppress_warning(struct kunit *test)
> +{
> + struct __suppressed_warning *warning;
> + int ret;
> +
> + warning = kunit_kzalloc(test, sizeof(*warning), GFP_KERNEL);
> + if (!warning)
> + return NULL;
> +
> + warning->task = current;
> + list_add_rcu(&warning->node, &suppressed_warnings);
> +
> + ret = kunit_add_action_or_reset(test,
> + __kunit_suppress_warning_cleanup,
> + warning);
> + if (ret)
> + return NULL;
> +
> + return warning;
> +}
> +EXPORT_SYMBOL_GPL(__kunit_start_suppress_warning);
> +
> +void __kunit_end_suppress_warning(struct kunit *test,
> + struct __suppressed_warning *warning)
> +{
> + if (!warning)
> + return;
> + kunit_release_action(test, __kunit_suppress_warning_cleanup, warning);
> +}
> +EXPORT_SYMBOL_GPL(__kunit_end_suppress_warning);
> +
> +int __kunit_suppressed_warning_count(struct __suppressed_warning *warning)
> +{
> + return warning ? warning->counter : 0;
> +}
> +EXPORT_SYMBOL_GPL(__kunit_suppressed_warning_count);
> +
> +bool __kunit_is_suppressed_warning(void)
> +{
> + struct __suppressed_warning *warning;
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> + if (warning->task == current) {
> + warning->counter++;
> + rcu_read_unlock();
> + return true;
> + }
> + }
> + rcu_read_unlock();
> +
> + return false;
> +}
Note to self: this is _not_ exported, as bug.c is being built-in
regardless of whether or not KUnit is a module. If we used the hook
system, it could live in kunit.ko, and would be manually exported by
kunit_install_hooks()
> +
> +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
>
Thanks again,
-- David
^ permalink raw reply [flat|nested] 20+ messages in thread
* [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression
2026-04-20 12:28 [PATCH v7 0/5] kunit: Add support for suppressing warning backtraces Albert Esteve
2026-04-20 12:28 ` [PATCH v7 1/5] bug/kunit: Core " Albert Esteve
@ 2026-04-20 12:28 ` Albert Esteve
2026-04-20 14:44 ` Peter Zijlstra
2026-04-22 12:19 ` David Gow
2026-04-20 12:28 ` [PATCH v7 3/5] kunit: Add backtrace suppression self-tests Albert Esteve
` (2 subsequent siblings)
4 siblings, 2 replies; 20+ messages in thread
From: Albert Esteve @ 2026-04-20 12:28 UTC (permalink / raw)
To: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Alessandro Carminati, Albert Esteve
From: Alessandro Carminati <acarmina@redhat.com>
KUnit support is not consistently present across distributions, some
include it in their stock kernels, while others do not.
While both KUNIT and KUNIT_SUPPRESS_BACKTRACE can be considered debug
features, the fact that some distros ship with KUnit enabled means it's
important to minimize the runtime impact of this patch.
To that end, this patch adds an atomic counter that tracks the number
of active suppressions. __kunit_is_suppressed_warning() checks this
counter first and returns immediately when no suppressions are active,
avoiding RCU-protected list traversal in the common case.
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
lib/kunit/bug.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
index 356c8a5928828..a7a88f0670d44 100644
--- a/lib/kunit/bug.c
+++ b/lib/kunit/bug.c
@@ -8,6 +8,7 @@
#include <kunit/bug.h>
#include <kunit/resource.h>
+#include <linux/atomic.h>
#include <linux/export.h>
#include <linux/rculist.h>
#include <linux/sched.h>
@@ -15,11 +16,13 @@
#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
static LIST_HEAD(suppressed_warnings);
+static atomic_t suppressed_warnings_cnt = ATOMIC_INIT(0);
static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
{
list_del_rcu(&warning->node);
synchronize_rcu(); /* Wait for readers to finish */
+ atomic_dec(&suppressed_warnings_cnt);
}
KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
@@ -37,6 +40,7 @@ __kunit_start_suppress_warning(struct kunit *test)
return NULL;
warning->task = current;
+ atomic_inc(&suppressed_warnings_cnt);
list_add_rcu(&warning->node, &suppressed_warnings);
ret = kunit_add_action_or_reset(test,
@@ -68,6 +72,9 @@ bool __kunit_is_suppressed_warning(void)
{
struct __suppressed_warning *warning;
+ if (!atomic_read(&suppressed_warnings_cnt))
+ return false;
+
rcu_read_lock();
list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
if (warning->task == current) {
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread* Re: [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression
2026-04-20 12:28 ` [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression Albert Esteve
@ 2026-04-20 14:44 ` Peter Zijlstra
2026-04-21 8:41 ` Albert Esteve
2026-04-22 12:19 ` David Gow
1 sibling, 1 reply; 20+ messages in thread
From: Peter Zijlstra @ 2026-04-20 14:44 UTC (permalink / raw)
To: Albert Esteve
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati
On Mon, Apr 20, 2026 at 02:28:04PM +0200, Albert Esteve wrote:
> From: Alessandro Carminati <acarmina@redhat.com>
>
> KUnit support is not consistently present across distributions, some
> include it in their stock kernels, while others do not.
> While both KUNIT and KUNIT_SUPPRESS_BACKTRACE can be considered debug
> features, the fact that some distros ship with KUnit enabled means it's
> important to minimize the runtime impact of this patch.
>
> To that end, this patch adds an atomic counter that tracks the number
> of active suppressions. __kunit_is_suppressed_warning() checks this
> counter first and returns immediately when no suppressions are active,
> avoiding RCU-protected list traversal in the common case.
>
> Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
> lib/kunit/bug.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
> index 356c8a5928828..a7a88f0670d44 100644
> --- a/lib/kunit/bug.c
> +++ b/lib/kunit/bug.c
> @@ -8,6 +8,7 @@
>
> #include <kunit/bug.h>
> #include <kunit/resource.h>
> +#include <linux/atomic.h>
> #include <linux/export.h>
> #include <linux/rculist.h>
> #include <linux/sched.h>
> @@ -15,11 +16,13 @@
> #ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
>
> static LIST_HEAD(suppressed_warnings);
> +static atomic_t suppressed_warnings_cnt = ATOMIC_INIT(0);
>
> static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
> {
> list_del_rcu(&warning->node);
> synchronize_rcu(); /* Wait for readers to finish */
> + atomic_dec(&suppressed_warnings_cnt);
> }
>
> KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
> @@ -37,6 +40,7 @@ __kunit_start_suppress_warning(struct kunit *test)
> return NULL;
>
> warning->task = current;
> + atomic_inc(&suppressed_warnings_cnt);
> list_add_rcu(&warning->node, &suppressed_warnings);
>
> ret = kunit_add_action_or_reset(test,
> @@ -68,6 +72,9 @@ bool __kunit_is_suppressed_warning(void)
> {
> struct __suppressed_warning *warning;
>
> + if (!atomic_read(&suppressed_warnings_cnt))
> + return false;
> +
> rcu_read_lock();
> list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> if (warning->task == current) {
>
So the thing you're skipping is:
rcu_read_lock();
list_for_each_entry_rcu() {
}
rcu_read_unlock();
Which is really cheap. Did you actually have performance numbers for
this?
A possibly better option is to add a static_branch() that could elide
any and all memory access.
^ permalink raw reply [flat|nested] 20+ messages in thread* Re: [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression
2026-04-20 14:44 ` Peter Zijlstra
@ 2026-04-21 8:41 ` Albert Esteve
0 siblings, 0 replies; 20+ messages in thread
From: Albert Esteve @ 2026-04-21 8:41 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati
On Mon, Apr 20, 2026 at 4:45 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Apr 20, 2026 at 02:28:04PM +0200, Albert Esteve wrote:
> > From: Alessandro Carminati <acarmina@redhat.com>
> >
> > KUnit support is not consistently present across distributions, some
> > include it in their stock kernels, while others do not.
> > While both KUNIT and KUNIT_SUPPRESS_BACKTRACE can be considered debug
> > features, the fact that some distros ship with KUnit enabled means it's
> > important to minimize the runtime impact of this patch.
> >
> > To that end, this patch adds an atomic counter that tracks the number
> > of active suppressions. __kunit_is_suppressed_warning() checks this
> > counter first and returns immediately when no suppressions are active,
> > avoiding RCU-protected list traversal in the common case.
> >
> > Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> > Signed-off-by: Albert Esteve <aesteve@redhat.com>
> > ---
> > lib/kunit/bug.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
> > index 356c8a5928828..a7a88f0670d44 100644
> > --- a/lib/kunit/bug.c
> > +++ b/lib/kunit/bug.c
> > @@ -8,6 +8,7 @@
> >
> > #include <kunit/bug.h>
> > #include <kunit/resource.h>
> > +#include <linux/atomic.h>
> > #include <linux/export.h>
> > #include <linux/rculist.h>
> > #include <linux/sched.h>
> > @@ -15,11 +16,13 @@
> > #ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> >
> > static LIST_HEAD(suppressed_warnings);
> > +static atomic_t suppressed_warnings_cnt = ATOMIC_INIT(0);
> >
> > static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
> > {
> > list_del_rcu(&warning->node);
> > synchronize_rcu(); /* Wait for readers to finish */
> > + atomic_dec(&suppressed_warnings_cnt);
> > }
> >
> > KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
> > @@ -37,6 +40,7 @@ __kunit_start_suppress_warning(struct kunit *test)
> > return NULL;
> >
> > warning->task = current;
> > + atomic_inc(&suppressed_warnings_cnt);
> > list_add_rcu(&warning->node, &suppressed_warnings);
> >
> > ret = kunit_add_action_or_reset(test,
> > @@ -68,6 +72,9 @@ bool __kunit_is_suppressed_warning(void)
> > {
> > struct __suppressed_warning *warning;
> >
> > + if (!atomic_read(&suppressed_warnings_cnt))
> > + return false;
> > +
> > rcu_read_lock();
> > list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> > if (warning->task == current) {
> >
>
> So the thing you're skipping is:
>
> rcu_read_lock();
> list_for_each_entry_rcu() {
> }
> rcu_read_unlock();
>
> Which is really cheap. Did you actually have performance numbers for
> this?
No, I do not have performance numbers. I kept the counter and the
separate patch for consistency with the previous version of the
series. But you have a good point, the skipped part is really cheap.
>
> A possibly better option is to add a static_branch() that could elide
> any and all memory access.
>
Previous version had static_branch and I removed it because I
understood from the discussion that the gains would not be significant
as performance gains are irrelevant in warn slowpath. But I think it
would make sense for a disabled feature. I will rework this for the
next version, remove the counter and use static_branch as suggested.
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression
2026-04-20 12:28 ` [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression Albert Esteve
2026-04-20 14:44 ` Peter Zijlstra
@ 2026-04-22 12:19 ` David Gow
1 sibling, 0 replies; 20+ messages in thread
From: David Gow @ 2026-04-22 12:19 UTC (permalink / raw)
To: Albert Esteve, Arnd Bergmann, Brendan Higgins, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Alessandro Carminati
Le 20/04/2026 à 8:28 PM, Albert Esteve a écrit :
> From: Alessandro Carminati <acarmina@redhat.com>
>
> KUnit support is not consistently present across distributions, some
> include it in their stock kernels, while others do not.
> While both KUNIT and KUNIT_SUPPRESS_BACKTRACE can be considered debug
> features, the fact that some distros ship with KUnit enabled means it's
> important to minimize the runtime impact of this patch.
>
> To that end, this patch adds an atomic counter that tracks the number
> of active suppressions. __kunit_is_suppressed_warning() checks this
> counter first and returns immediately when no suppressions are active,
> avoiding RCU-protected list traversal in the common case.
>
> Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
I'm not sure how much of an improvement this is.
It might be worth putting things behind the kunit_running static branch.
You could even add a new kunit_has_suppressed_warnings static branch,
though I doubt anyone's too worried about the runtime performance of
WARN() during testing, but with no suppressions, so it's likely not
worth it.
Have a look at, e.g., kunit_fail_current_test() in
include/kunit/test-bug.h, which uses the existing hooks implementation
and static branch to reduce the overhead as much as I'd expect we need.
That'd also potentially let you move the backtrace suppression code into
the kunit.ko module, so you're not even paying more than ~a pointer's
worth of memory if no tests are even loaded.
Cheers,
-- David
^ permalink raw reply [flat|nested] 20+ messages in thread
* [PATCH v7 3/5] kunit: Add backtrace suppression self-tests
2026-04-20 12:28 [PATCH v7 0/5] kunit: Add support for suppressing warning backtraces Albert Esteve
2026-04-20 12:28 ` [PATCH v7 1/5] bug/kunit: Core " Albert Esteve
2026-04-20 12:28 ` [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression Albert Esteve
@ 2026-04-20 12:28 ` Albert Esteve
2026-04-22 12:20 ` David Gow
2026-04-20 12:28 ` [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests Albert Esteve
2026-04-20 12:28 ` [PATCH v7 5/5] kunit: Add documentation for warning backtrace suppression API Albert Esteve
4 siblings, 1 reply; 20+ messages in thread
From: Albert Esteve @ 2026-04-20 12:28 UTC (permalink / raw)
To: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter,
Alessandro Carminati, Albert Esteve, Kees Cook
From: Guenter Roeck <linux@roeck-us.net>
Add unit tests to verify that warning backtrace suppression works,
covering WARN() and WARN_ON() with direct calls, indirect calls
through helper functions, and multiple warnings in a single window.
If backtrace suppression does _not_ work, the unit tests will likely
trigger unsuppressed backtraces, which should actually help to get
the affected architectures / platforms fixed.
Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
lib/kunit/Makefile | 3 ++
lib/kunit/backtrace-suppression-test.c | 90 ++++++++++++++++++++++++++++++++++
2 files changed, 93 insertions(+)
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index fe177ff3ebdef..b2f2b8ada7b71 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -23,6 +23,9 @@ obj-$(if $(CONFIG_KUNIT),y) += hooks.o \
obj-$(CONFIG_KUNIT_TEST) += kunit-test.o
obj-$(CONFIG_KUNIT_TEST) += platform-test.o
+ifeq ($(CONFIG_KUNIT_SUPPRESS_BACKTRACE),y)
+obj-$(CONFIG_KUNIT_TEST) += backtrace-suppression-test.o
+endif
# string-stream-test compiles built-in only.
ifeq ($(CONFIG_KUNIT_TEST),y)
diff --git a/lib/kunit/backtrace-suppression-test.c b/lib/kunit/backtrace-suppression-test.c
new file mode 100644
index 0000000000000..2ba5dcb5fef35
--- /dev/null
+++ b/lib/kunit/backtrace-suppression-test.c
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for suppressing warning tracebacks.
+ *
+ * Copyright (C) 2024, Guenter Roeck
+ * Author: Guenter Roeck <linux@roeck-us.net>
+ */
+
+#include <kunit/test.h>
+#include <linux/bug.h>
+
+static void backtrace_suppression_test_warn_direct(struct kunit *test)
+{
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ WARN(1, "This backtrace should be suppressed");
+ KUNIT_END_SUPPRESSED_WARNING(test);
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
+}
+
+static void trigger_backtrace_warn(void)
+{
+ WARN(1, "This backtrace should be suppressed");
+}
+
+static void backtrace_suppression_test_warn_indirect(struct kunit *test)
+{
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ trigger_backtrace_warn();
+ KUNIT_END_SUPPRESSED_WARNING(test);
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
+}
+
+static void backtrace_suppression_test_warn_multi(struct kunit *test)
+{
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ WARN(1, "This backtrace should be suppressed");
+ trigger_backtrace_warn();
+ KUNIT_END_SUPPRESSED_WARNING(test);
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 2);
+}
+
+static void backtrace_suppression_test_warn_on_direct(struct kunit *test)
+{
+ if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE) && !IS_ENABLED(CONFIG_KALLSYMS))
+ kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE or CONFIG_KALLSYMS");
+
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ WARN_ON(1);
+ KUNIT_END_SUPPRESSED_WARNING(test);
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
+}
+
+static void trigger_backtrace_warn_on(void)
+{
+ WARN_ON(1);
+}
+
+static void backtrace_suppression_test_warn_on_indirect(struct kunit *test)
+{
+ if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE))
+ kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE");
+
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ trigger_backtrace_warn_on();
+ KUNIT_END_SUPPRESSED_WARNING(test);
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
+}
+
+static struct kunit_case backtrace_suppression_test_cases[] = {
+ KUNIT_CASE(backtrace_suppression_test_warn_direct),
+ KUNIT_CASE(backtrace_suppression_test_warn_indirect),
+ KUNIT_CASE(backtrace_suppression_test_warn_multi),
+ KUNIT_CASE(backtrace_suppression_test_warn_on_direct),
+ KUNIT_CASE(backtrace_suppression_test_warn_on_indirect),
+ {}
+};
+
+static struct kunit_suite backtrace_suppression_test_suite = {
+ .name = "backtrace-suppression-test",
+ .test_cases = backtrace_suppression_test_cases,
+};
+kunit_test_suites(&backtrace_suppression_test_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("KUnit test to verify warning backtrace suppression");
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread* Re: [PATCH v7 3/5] kunit: Add backtrace suppression self-tests
2026-04-20 12:28 ` [PATCH v7 3/5] kunit: Add backtrace suppression self-tests Albert Esteve
@ 2026-04-22 12:20 ` David Gow
0 siblings, 0 replies; 20+ messages in thread
From: David Gow @ 2026-04-22 12:20 UTC (permalink / raw)
To: Albert Esteve, Arnd Bergmann, Brendan Higgins, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter,
Alessandro Carminati, Kees Cook
Le 20/04/2026 à 8:28 PM, Albert Esteve a écrit :
> From: Guenter Roeck <linux@roeck-us.net>
>
> Add unit tests to verify that warning backtrace suppression works,
> covering WARN() and WARN_ON() with direct calls, indirect calls
> through helper functions, and multiple warnings in a single window.
>
> If backtrace suppression does _not_ work, the unit tests will likely
> trigger unsuppressed backtraces, which should actually help to get
> the affected architectures / platforms fixed.
>
> Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
> Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
Thanks very much for including tests!
Maybe it'd be nice to test that the suppression is disabled after
KUNIT_END_SUPPRESSED_WARNING(). Of course, then triggering an actual
stacktrace would be a pain, but maybe we could check that
__kunit_is_suppressed_warning() returns false? If you wanted to be
really fancy, you could test that it returns false on another kthread
even while the suppression is active, too, but I won't hold you to it.
Equally, you could try setting up a fake test context and ensuring the
cleanup is called correctly, but I think that's mostly covered by the
existing KUnit resource tests.
Otherwise, looking good. A couple of other minor suggestions below,
which may require some reworking of the __kunit_suppress scope, but all
optional suggestions.
Reviewed-by: David Gow <david@davidgow.net>
> lib/kunit/Makefile | 3 ++
> lib/kunit/backtrace-suppression-test.c | 90 ++++++++++++++++++++++++++++++++++
> 2 files changed, 93 insertions(+)
>
> diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
> index fe177ff3ebdef..b2f2b8ada7b71 100644
> --- a/lib/kunit/Makefile
> +++ b/lib/kunit/Makefile
> @@ -23,6 +23,9 @@ obj-$(if $(CONFIG_KUNIT),y) += hooks.o \
>
> obj-$(CONFIG_KUNIT_TEST) += kunit-test.o
> obj-$(CONFIG_KUNIT_TEST) += platform-test.o
> +ifeq ($(CONFIG_KUNIT_SUPPRESS_BACKTRACE),y)
> +obj-$(CONFIG_KUNIT_TEST) += backtrace-suppression-test.o
> +endif
>
> # string-stream-test compiles built-in only.
> ifeq ($(CONFIG_KUNIT_TEST),y)
> diff --git a/lib/kunit/backtrace-suppression-test.c b/lib/kunit/backtrace-suppression-test.c
> new file mode 100644
> index 0000000000000..2ba5dcb5fef35
> --- /dev/null
> +++ b/lib/kunit/backtrace-suppression-test.c
> @@ -0,0 +1,90 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KUnit test for suppressing warning tracebacks.
> + *
> + * Copyright (C) 2024, Guenter Roeck
> + * Author: Guenter Roeck <linux@roeck-us.net>
> + */
> +
> +#include <kunit/test.h>
> +#include <linux/bug.h>
> +
> +static void backtrace_suppression_test_warn_direct(struct kunit *test)
> +{
> + KUNIT_START_SUPPRESSED_WARNING(test);
> + WARN(1, "This backtrace should be suppressed");
> + KUNIT_END_SUPPRESSED_WARNING(test);
> +
> + KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
> +}
> +
> +static void trigger_backtrace_warn(void)
> +{
> + WARN(1, "This backtrace should be suppressed");
> +}
> +
> +static void backtrace_suppression_test_warn_indirect(struct kunit *test)
> +{
> + KUNIT_START_SUPPRESSED_WARNING(test);
> + trigger_backtrace_warn();
> + KUNIT_END_SUPPRESSED_WARNING(test);
> +
> + KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
> +}
> +
> +static void backtrace_suppression_test_warn_multi(struct kunit *test)
> +{
> + KUNIT_START_SUPPRESSED_WARNING(test);
> + WARN(1, "This backtrace should be suppressed");
> + trigger_backtrace_warn();
> + KUNIT_END_SUPPRESSED_WARNING(test);
> +
> + KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 2);
Would it make sense to test KUNIT_SUPPRESSED_WARNING_COUNT() more
thoroughly here by checking that it's 0 before any warnings, and
checking that it's 1 in-between the two warnings?
Of course, the first case doesn't work due to __kunit_suppress not being
defined, but if the implementation changes to support this, let's add it
to the test, too.
> +}
> +
> +static void backtrace_suppression_test_warn_on_direct(struct kunit *test)
> +{
> + if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE) && !IS_ENABLED(CONFIG_KALLSYMS))
> + kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE or CONFIG_KALLSYMS");
> +
> + KUNIT_START_SUPPRESSED_WARNING(test);
> + WARN_ON(1);
> + KUNIT_END_SUPPRESSED_WARNING(test);
> +
> + KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
> +}
> +
> +static void trigger_backtrace_warn_on(void)
> +{
> + WARN_ON(1);
> +}
> +
> +static void backtrace_suppression_test_warn_on_indirect(struct kunit *test)
> +{
> + if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE))
> + kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE");
> +
> + KUNIT_START_SUPPRESSED_WARNING(test);
> + trigger_backtrace_warn_on();
> + KUNIT_END_SUPPRESSED_WARNING(test);
> +
> + KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
> +}
> +
> +static struct kunit_case backtrace_suppression_test_cases[] = {
> + KUNIT_CASE(backtrace_suppression_test_warn_direct),
> + KUNIT_CASE(backtrace_suppression_test_warn_indirect),
> + KUNIT_CASE(backtrace_suppression_test_warn_multi),
> + KUNIT_CASE(backtrace_suppression_test_warn_on_direct),
> + KUNIT_CASE(backtrace_suppression_test_warn_on_indirect),
> + {}
> +};
> +
> +static struct kunit_suite backtrace_suppression_test_suite = {
> + .name = "backtrace-suppression-test",
> + .test_cases = backtrace_suppression_test_cases,
> +};
> +kunit_test_suites(&backtrace_suppression_test_suite);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("KUnit test to verify warning backtrace suppression");
>
^ permalink raw reply [flat|nested] 20+ messages in thread
* [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests
2026-04-20 12:28 [PATCH v7 0/5] kunit: Add support for suppressing warning backtraces Albert Esteve
` (2 preceding siblings ...)
2026-04-20 12:28 ` [PATCH v7 3/5] kunit: Add backtrace suppression self-tests Albert Esteve
@ 2026-04-20 12:28 ` Albert Esteve
2026-04-20 14:47 ` Peter Zijlstra
2026-04-22 12:20 ` David Gow
2026-04-20 12:28 ` [PATCH v7 5/5] kunit: Add documentation for warning backtrace suppression API Albert Esteve
4 siblings, 2 replies; 20+ messages in thread
From: Albert Esteve @ 2026-04-20 12:28 UTC (permalink / raw)
To: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter, Maíra Canal,
Alessandro Carminati, Albert Esteve, Simona Vetter
From: Guenter Roeck <linux@roeck-us.net>
The drm_test_rect_calc_hscale and drm_test_rect_calc_vscale unit tests
intentionally trigger warning backtraces by providing bad parameters to
the tested functions. What is tested is the return value, not the existence
of a warning backtrace. Suppress the backtraces to avoid clogging the
kernel log and distraction from real problems.
Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Maíra Canal <mcanal@igalia.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
drivers/gpu/drm/tests/drm_rect_test.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/drivers/gpu/drm/tests/drm_rect_test.c b/drivers/gpu/drm/tests/drm_rect_test.c
index 17e1f34b76101..1dd7d819165e7 100644
--- a/drivers/gpu/drm/tests/drm_rect_test.c
+++ b/drivers/gpu/drm/tests/drm_rect_test.c
@@ -409,8 +409,15 @@ static void drm_test_rect_calc_hscale(struct kunit *test)
const struct drm_rect_scale_case *params = test->param_value;
int scaling_factor;
+ /*
+ * drm_rect_calc_hscale() generates a warning backtrace whenever bad
+ * parameters are passed to it. This affects all unit tests with an
+ * error code in expected_scaling_factor.
+ */
+ KUNIT_START_SUPPRESSED_WARNING(test);
scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
params->min_range, params->max_range);
+ KUNIT_END_SUPPRESSED_WARNING(test);
KUNIT_EXPECT_EQ(test, scaling_factor, params->expected_scaling_factor);
}
@@ -420,8 +427,15 @@ static void drm_test_rect_calc_vscale(struct kunit *test)
const struct drm_rect_scale_case *params = test->param_value;
int scaling_factor;
+ /*
+ * drm_rect_calc_vscale() generates a warning backtrace whenever bad
+ * parameters are passed to it. This affects all unit tests with an
+ * error code in expected_scaling_factor.
+ */
+ KUNIT_START_SUPPRESSED_WARNING(test);
scaling_factor = drm_rect_calc_vscale(¶ms->src, ¶ms->dst,
params->min_range, params->max_range);
+ KUNIT_END_SUPPRESSED_WARNING(test);
KUNIT_EXPECT_EQ(test, scaling_factor, params->expected_scaling_factor);
}
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread* Re: [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests
2026-04-20 12:28 ` [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests Albert Esteve
@ 2026-04-20 14:47 ` Peter Zijlstra
2026-04-21 8:49 ` Albert Esteve
2026-04-22 12:20 ` David Gow
1 sibling, 1 reply; 20+ messages in thread
From: Peter Zijlstra @ 2026-04-20 14:47 UTC (permalink / raw)
To: Albert Esteve
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter, Maíra Canal,
Alessandro Carminati, Simona Vetter
On Mon, Apr 20, 2026 at 02:28:06PM +0200, Albert Esteve wrote:
> From: Guenter Roeck <linux@roeck-us.net>
>
> The drm_test_rect_calc_hscale and drm_test_rect_calc_vscale unit tests
> intentionally trigger warning backtraces by providing bad parameters to
> the tested functions. What is tested is the return value, not the existence
> of a warning backtrace. Suppress the backtraces to avoid clogging the
> kernel log and distraction from real problems.
>
> Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
> Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
> Acked-by: Maíra Canal <mcanal@igalia.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
> drivers/gpu/drm/tests/drm_rect_test.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/drivers/gpu/drm/tests/drm_rect_test.c b/drivers/gpu/drm/tests/drm_rect_test.c
> index 17e1f34b76101..1dd7d819165e7 100644
> --- a/drivers/gpu/drm/tests/drm_rect_test.c
> +++ b/drivers/gpu/drm/tests/drm_rect_test.c
> @@ -409,8 +409,15 @@ static void drm_test_rect_calc_hscale(struct kunit *test)
> const struct drm_rect_scale_case *params = test->param_value;
> int scaling_factor;
>
> + /*
> + * drm_rect_calc_hscale() generates a warning backtrace whenever bad
> + * parameters are passed to it. This affects all unit tests with an
> + * error code in expected_scaling_factor.
> + */
> + KUNIT_START_SUPPRESSED_WARNING(test);
> scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
> params->min_range, params->max_range);
> + KUNIT_END_SUPPRESSED_WARNING(test);
Would not something like:
scoped_kunit_suppress() {
scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
params->min_range, params->max_range);
}
be better?
Also, how can you stand all this screaming in the code?
^ permalink raw reply [flat|nested] 20+ messages in thread* Re: [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests
2026-04-20 14:47 ` Peter Zijlstra
@ 2026-04-21 8:49 ` Albert Esteve
2026-04-21 11:50 ` Jani Nikula
0 siblings, 1 reply; 20+ messages in thread
From: Albert Esteve @ 2026-04-21 8:49 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter, Maíra Canal,
Alessandro Carminati, Simona Vetter
On Mon, Apr 20, 2026 at 4:47 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Apr 20, 2026 at 02:28:06PM +0200, Albert Esteve wrote:
> > From: Guenter Roeck <linux@roeck-us.net>
> >
> > The drm_test_rect_calc_hscale and drm_test_rect_calc_vscale unit tests
> > intentionally trigger warning backtraces by providing bad parameters to
> > the tested functions. What is tested is the return value, not the existence
> > of a warning backtrace. Suppress the backtraces to avoid clogging the
> > kernel log and distraction from real problems.
> >
> > Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
> > Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
> > Acked-by: Maíra Canal <mcanal@igalia.com>
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: David Airlie <airlied@gmail.com>
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> > Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> > Signed-off-by: Albert Esteve <aesteve@redhat.com>
> > ---
> > drivers/gpu/drm/tests/drm_rect_test.c | 14 ++++++++++++++
> > 1 file changed, 14 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/tests/drm_rect_test.c b/drivers/gpu/drm/tests/drm_rect_test.c
> > index 17e1f34b76101..1dd7d819165e7 100644
> > --- a/drivers/gpu/drm/tests/drm_rect_test.c
> > +++ b/drivers/gpu/drm/tests/drm_rect_test.c
> > @@ -409,8 +409,15 @@ static void drm_test_rect_calc_hscale(struct kunit *test)
> > const struct drm_rect_scale_case *params = test->param_value;
> > int scaling_factor;
> >
> > + /*
> > + * drm_rect_calc_hscale() generates a warning backtrace whenever bad
> > + * parameters are passed to it. This affects all unit tests with an
> > + * error code in expected_scaling_factor.
> > + */
> > + KUNIT_START_SUPPRESSED_WARNING(test);
> > scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
> > params->min_range, params->max_range);
> > + KUNIT_END_SUPPRESSED_WARNING(test);
>
> Would not something like:
>
> scoped_kunit_suppress() {
> scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
> params->min_range, params->max_range);
> }
>
> be better?
Since KUnit already has a few macros in its API it didn't occur to me.
Good idea, I like it. And I guess the scope approach matches well with
your __cleanup comment in the first patch. If no one opposes, I will
work toward that pattern for the next version.
>
> Also, how can you stand all this screaming in the code?
>
Again, KUnit already contains many macros, so this use didn't register
as such. Now I will not be able to unsee it.
^ permalink raw reply [flat|nested] 20+ messages in thread* Re: [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests
2026-04-21 8:49 ` Albert Esteve
@ 2026-04-21 11:50 ` Jani Nikula
0 siblings, 0 replies; 20+ messages in thread
From: Jani Nikula @ 2026-04-21 11:50 UTC (permalink / raw)
To: Albert Esteve, Peter Zijlstra
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter, Maíra Canal,
Alessandro Carminati, Simona Vetter
On Tue, 21 Apr 2026, Albert Esteve <aesteve@redhat.com> wrote:
> On Mon, Apr 20, 2026 at 4:47 PM Peter Zijlstra <peterz@infradead.org> wrote:
>>
>> On Mon, Apr 20, 2026 at 02:28:06PM +0200, Albert Esteve wrote:
>> > From: Guenter Roeck <linux@roeck-us.net>
>> >
>> > The drm_test_rect_calc_hscale and drm_test_rect_calc_vscale unit tests
>> > intentionally trigger warning backtraces by providing bad parameters to
>> > the tested functions. What is tested is the return value, not the existence
>> > of a warning backtrace. Suppress the backtraces to avoid clogging the
>> > kernel log and distraction from real problems.
>> >
>> > Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
>> > Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
>> > Acked-by: Maíra Canal <mcanal@igalia.com>
>> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> > Cc: David Airlie <airlied@gmail.com>
>> > Cc: Daniel Vetter <daniel@ffwll.ch>
>> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
>> > Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
>> > Signed-off-by: Albert Esteve <aesteve@redhat.com>
>> > ---
>> > drivers/gpu/drm/tests/drm_rect_test.c | 14 ++++++++++++++
>> > 1 file changed, 14 insertions(+)
>> >
>> > diff --git a/drivers/gpu/drm/tests/drm_rect_test.c b/drivers/gpu/drm/tests/drm_rect_test.c
>> > index 17e1f34b76101..1dd7d819165e7 100644
>> > --- a/drivers/gpu/drm/tests/drm_rect_test.c
>> > +++ b/drivers/gpu/drm/tests/drm_rect_test.c
>> > @@ -409,8 +409,15 @@ static void drm_test_rect_calc_hscale(struct kunit *test)
>> > const struct drm_rect_scale_case *params = test->param_value;
>> > int scaling_factor;
>> >
>> > + /*
>> > + * drm_rect_calc_hscale() generates a warning backtrace whenever bad
>> > + * parameters are passed to it. This affects all unit tests with an
>> > + * error code in expected_scaling_factor.
>> > + */
>> > + KUNIT_START_SUPPRESSED_WARNING(test);
>> > scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
>> > params->min_range, params->max_range);
>> > + KUNIT_END_SUPPRESSED_WARNING(test);
>>
>> Would not something like:
>>
>> scoped_kunit_suppress() {
>> scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
>> params->min_range, params->max_range);
>> }
>>
>> be better?
>
> Since KUnit already has a few macros in its API it didn't occur to me.
> Good idea, I like it. And I guess the scope approach matches well with
> your __cleanup comment in the first patch. If no one opposes, I will
> work toward that pattern for the next version.
There's a catch with kunit and __cleanup and thus (scoped) guards. Kunit
runs in ktreads, asserts lead to kthread_exit() and the __cleanup won't
be called.
Warning suppression being part of kunit infrastructure, asserts can and
should end the suppression too. But setting the example (scoped) guards
are safe in kunit tests in general feels like a trap waiting to happen.
BR,
Jani.
>
>>
>> Also, how can you stand all this screaming in the code?
>>
>
> Again, KUnit already contains many macros, so this use didn't register
> as such. Now I will not be able to unsee it.
>
>
--
Jani Nikula, Intel
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests
2026-04-20 12:28 ` [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests Albert Esteve
2026-04-20 14:47 ` Peter Zijlstra
@ 2026-04-22 12:20 ` David Gow
1 sibling, 0 replies; 20+ messages in thread
From: David Gow @ 2026-04-22 12:20 UTC (permalink / raw)
To: Albert Esteve, Arnd Bergmann, Brendan Higgins, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter, Maíra Canal,
Alessandro Carminati, Simona Vetter
Le 20/04/2026 à 8:28 PM, Albert Esteve a écrit :
> From: Guenter Roeck <linux@roeck-us.net>
>
> The drm_test_rect_calc_hscale and drm_test_rect_calc_vscale unit tests
> intentionally trigger warning backtraces by providing bad parameters to
> the tested functions. What is tested is the return value, not the existence
> of a warning backtrace. Suppress the backtraces to avoid clogging the
> kernel log and distraction from real problems.
>
> Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
> Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
> Acked-by: Maíra Canal <mcanal@igalia.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
Acked-by: David Gow <david@davidgow.net>
Some of the suggestions in the thread around __cleanup() et al. sound
good to me, too. I suspect that it should work given the
kunit_add_action() / resource system use anyway, so even if an assertion
fires, things should be cleaned up properly.
Cheers,
-- David
> drivers/gpu/drm/tests/drm_rect_test.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/drivers/gpu/drm/tests/drm_rect_test.c b/drivers/gpu/drm/tests/drm_rect_test.c
> index 17e1f34b76101..1dd7d819165e7 100644
> --- a/drivers/gpu/drm/tests/drm_rect_test.c
> +++ b/drivers/gpu/drm/tests/drm_rect_test.c
> @@ -409,8 +409,15 @@ static void drm_test_rect_calc_hscale(struct kunit *test)
> const struct drm_rect_scale_case *params = test->param_value;
> int scaling_factor;
>
> + /*
> + * drm_rect_calc_hscale() generates a warning backtrace whenever bad
> + * parameters are passed to it. This affects all unit tests with an
> + * error code in expected_scaling_factor.
> + */
> + KUNIT_START_SUPPRESSED_WARNING(test);
> scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
> params->min_range, params->max_range);
> + KUNIT_END_SUPPRESSED_WARNING(test);
>
> KUNIT_EXPECT_EQ(test, scaling_factor, params->expected_scaling_factor);
> }
> @@ -420,8 +427,15 @@ static void drm_test_rect_calc_vscale(struct kunit *test)
> const struct drm_rect_scale_case *params = test->param_value;
> int scaling_factor;
>
> + /*
> + * drm_rect_calc_vscale() generates a warning backtrace whenever bad
> + * parameters are passed to it. This affects all unit tests with an
> + * error code in expected_scaling_factor.
> + */
> + KUNIT_START_SUPPRESSED_WARNING(test);
> scaling_factor = drm_rect_calc_vscale(¶ms->src, ¶ms->dst,
> params->min_range, params->max_range);
> + KUNIT_END_SUPPRESSED_WARNING(test);
>
> KUNIT_EXPECT_EQ(test, scaling_factor, params->expected_scaling_factor);
> }
>
^ permalink raw reply [flat|nested] 20+ messages in thread
* [PATCH v7 5/5] kunit: Add documentation for warning backtrace suppression API
2026-04-20 12:28 [PATCH v7 0/5] kunit: Add support for suppressing warning backtraces Albert Esteve
` (3 preceding siblings ...)
2026-04-20 12:28 ` [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests Albert Esteve
@ 2026-04-20 12:28 ` Albert Esteve
2026-04-22 12:20 ` David Gow
4 siblings, 1 reply; 20+ messages in thread
From: Albert Esteve @ 2026-04-20 12:28 UTC (permalink / raw)
To: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter,
Alessandro Carminati, Albert Esteve, Kees Cook, David Gow
From: Guenter Roeck <linux@roeck-us.net>
Document API functions for suppressing warning backtraces.
Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
Documentation/dev-tools/kunit/usage.rst | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)
diff --git a/Documentation/dev-tools/kunit/usage.rst b/Documentation/dev-tools/kunit/usage.rst
index ebd06f5ea4550..76e85412f240e 100644
--- a/Documentation/dev-tools/kunit/usage.rst
+++ b/Documentation/dev-tools/kunit/usage.rst
@@ -157,6 +157,34 @@ Alternatively, one can take full control over the error message by using
if (some_setup_function())
KUNIT_FAIL(test, "Failed to setup thing for testing");
+Suppressing warning backtraces
+------------------------------
+
+Some unit tests trigger warning backtraces either intentionally or as side
+effect. Such backtraces are normally undesirable since they distract from
+the actual test and may result in the impression that there is a problem.
+
+Such backtraces can be suppressed with **task scope suppression**: while
+``START`` / ``END`` is active on the current task, the backtrace and stack
+dump from warnings on that task are suppressed. Wrap the call from your test
+in that window, like shown in the following code.
+
+.. code-block:: c
+
+ static void some_test(struct kunit *test)
+ {
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ trigger_backtrace();
+ KUNIT_END_SUPPRESSED_WARNING(test);
+ }
+
+``KUNIT_SUPPRESSED_WARNING_COUNT()`` returns the number of suppressed backtraces.
+If the suppressed backtrace was triggered on purpose, this can be used to check
+if the backtrace was actually triggered.
+
+.. code-block:: c
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
Test Suites
~~~~~~~~~~~
@@ -1211,4 +1239,4 @@ For example:
dev_managed_string = devm_kstrdup(fake_device, "Hello, World!");
// Everything is cleaned up automatically when the test ends.
- }
\ No newline at end of file
+ }
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread* Re: [PATCH v7 5/5] kunit: Add documentation for warning backtrace suppression API
2026-04-20 12:28 ` [PATCH v7 5/5] kunit: Add documentation for warning backtrace suppression API Albert Esteve
@ 2026-04-22 12:20 ` David Gow
0 siblings, 0 replies; 20+ messages in thread
From: David Gow @ 2026-04-22 12:20 UTC (permalink / raw)
To: Albert Esteve, Arnd Bergmann, Brendan Higgins, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter,
Alessandro Carminati, Kees Cook
Le 20/04/2026 à 8:28 PM, Albert Esteve a écrit :
> From: Guenter Roeck <linux@roeck-us.net>
>
> Document API functions for suppressing warning backtraces.
>
> Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
> Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> Reviewed-by: David Gow <davidgow@google.com>
> Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
Thanks -- it's always good to have documentation.
Apart from one note below, this looks good to me.
Reviewed-by: David Gow <david@davidgow.net>
Cheers,
-- David
> Documentation/dev-tools/kunit/usage.rst | 30 +++++++++++++++++++++++++++++-
> 1 file changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/dev-tools/kunit/usage.rst b/Documentation/dev-tools/kunit/usage.rst
> index ebd06f5ea4550..76e85412f240e 100644
> --- a/Documentation/dev-tools/kunit/usage.rst
> +++ b/Documentation/dev-tools/kunit/usage.rst
> @@ -157,6 +157,34 @@ Alternatively, one can take full control over the error message by using
> if (some_setup_function())
> KUNIT_FAIL(test, "Failed to setup thing for testing");
>
> +Suppressing warning backtraces
> +------------------------------
> +
> +Some unit tests trigger warning backtraces either intentionally or as side
> +effect. Such backtraces are normally undesirable since they distract from
> +the actual test and may result in the impression that there is a problem.
> +
> +Such backtraces can be suppressed with **task scope suppression**: while
> +``START`` / ``END`` is active on the current task, the backtrace and stack
> +dump from warnings on that task are suppressed. Wrap the call from your test
> +in that window, like shown in the following code.
> +
> +.. code-block:: c
> +
> + static void some_test(struct kunit *test)
> + {
> + KUNIT_START_SUPPRESSED_WARNING(test);
> + trigger_backtrace();
> + KUNIT_END_SUPPRESSED_WARNING(test);
> + }
> +
> +``KUNIT_SUPPRESSED_WARNING_COUNT()`` returns the number of suppressed backtraces.
> +If the suppressed backtrace was triggered on purpose, this can be used to check
> +if the backtrace was actually triggered.
> +
> +.. code-block:: c
> +
> + KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
It might be worth noting that all of these must be in the same function,
and the KUNIT_START_SUPPRESSED_WARNING() must be first. (And, in
addition, there can't be more than one START/END pair per-function).
Of course, if the implementation is changed, that wouldn't be necessary. :-)
>
> Test Suites
> ~~~~~~~~~~~
> @@ -1211,4 +1239,4 @@ For example:
> dev_managed_string = devm_kstrdup(fake_device, "Hello, World!");
>
> // Everything is cleaned up automatically when the test ends.
> - }
> \ No newline at end of file
> + }
>
^ permalink raw reply [flat|nested] 20+ messages in thread