On 3/14/24 08:02, Maxime Ripard wrote:
On Thu, Mar 14, 2024 at 07:37:13AM -0700, Guenter Roeck wrote:
On 3/14/24 06:36, Geert Uytterhoeven wrote:
Hi Günter,
On Tue, Mar 12, 2024 at 6:03 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
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.
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. Support suppressing multiple
backtraces while at the same time limiting changes to generic code to the
absolute minimum. Architecture specific changes are kept at minimum by
retaining function names only if both CONFIG_DEBUG_BUGVERBOSE and
CONFIG_KUNIT are enabled.
The first patch of the series introduces the necessary infrastructure.
The second patch introduces support for counting suppressed backtraces.
This capability is used in patch three to implement unit tests.
Patch four documents the new API.
The next two patches add support for suppressing backtraces in drm_rect
and dev_addr_lists unit tests. These patches are intended to serve as
examples for the use of the functionality introduced with this series.
The remaining patches implement the necessary changes for all
architectures with GENERIC_BUG support.
Thanks for your series!
I gave it a try on m68k, just running backtrace-suppression-test,
and that seems to work fine.
Design note:
Function pointers are only added to the __bug_table section if both
CONFIG_KUNIT and CONFIG_DEBUG_BUGVERBOSE are enabled to avoid image
size increases if CONFIG_KUNIT=n. There would be some benefits to
adding those pointers all the time (reduced complexity, ability to
display function names in BUG/WARNING messages). That change, if
desired, can be made later.
Unfortunately this also increases kernel size in the CONFIG_KUNIT=m
case (ca. 80 KiB for atari_defconfig), making it less attractive to have
kunit and all tests enabled as modules in my standard kernel.
Good point. Indeed, it does. I wanted to avoid adding a configuration option,
but maybe I should add it after all. How about something like this ?
+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 can be suppressed. Disable
+ to reduce kernel image size if image size is more important than
+ suppression of backtraces generated by KUnit tests.
+
How are tests using that API supposed to handle it then?
Select the config option or put an ifdef?
If the former, we end up in the same situation than without the symbol.
If the latter, we end up in a similar situation than disabling KUNIT
entirely, with some tests not being run which is just terrible.
The API definitions are themselves within #ifdef and dummies if
KUNIT_SUPPRESS_BACKTRACE (currently CONFIG_KUNIT) is disabled.
In include/kunit/bug.h:
#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
...
#else
#define DEFINE_SUPPRESSED_WARNING(func)
#define START_SUPPRESSED_WARNING(func)
#define END_SUPPRESSED_WARNING(func)
#define IS_SUPPRESSED_WARNING(func) (false)
#define SUPPRESSED_WARNING_COUNT(func) (0)
#endif
Only difference to the current patch series would be
- #if IS_ENABLED(CONFIG_KUNIT)
+ #ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
in that file and elsewhere.
With KUNIT_SUPPRESS_BACKTRACE=n you'd still get warning backtraces
triggered by the tests, but the number of tests executed as well
as the test results would still be the same.
Thanks,
Guenter
