On Wed, Apr 03, 2024 at 06:19:21AM -0700, Guenter Roeck 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. > > With CONFIG_KUNIT enabled, image size increase with this series applied is > approximately 1%. The image size increase (and with it the functionality > introduced by this series) can be avoided by disabling > CONFIG_KUNIT_SUPPRESS_BACKTRACE. > > This series is based on the RFC patch and subsequent discussion at > https://patchwork.kernel.org/project/linux-kselftest/patch/02546e59-1afe-4b08-ba81-d94f3b691c9a@moroto.mountain/ > and offers a more comprehensive solution of the problem discussed there. > > Design note: > Function pointers are only added to the __bug_table section if both > CONFIG_KUNIT_SUPPRESS_BACKTRACE and CONFIG_DEBUG_BUGVERBOSE are enabled > to avoid image size increases if CONFIG_KUNIT is disabled. 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. > > Checkpatch note: > Remaining checkpatch errors and warnings were deliberately ignored. > Some are triggered by matching coding style or by comments interpreted > as code, others by assembler macros which are disliked by checkpatch. > Suggestions for improvements are welcome. > > Changes since RFC: > - Introduced CONFIG_KUNIT_SUPPRESS_BACKTRACE > - Minor cleanups and bug fixes > - Added support for all affected architectures > - Added support for counting suppressed warnings > - Added unit tests using those counters > - Added patch to suppress warning backtraces in dev_addr_lists tests > > Changes since v1: > - Rebased to v6.9-rc1 > - Added Tested-by:, Acked-by:, and Reviewed-by: tags > [I retained those tags since there have been no functional changes] > - Introduced KUNIT_SUPPRESS_BACKTRACE configuration option, enabled by > default. > > Changes since v2: > - Rebased to v6.9-rc2 > - Added comments to drm warning suppression explaining why it is needed. > - Added patch to move conditional code in arch/sh/include/asm/bug.h > to avoid kerneldoc warning > - Added architecture maintainers to Cc: for architecture specific patches > - No functional changes > > ---------------------------------------------------------------- > Guenter Roeck (15): > bug/kunit: Core support for suppressing warning backtraces > kunit: bug: Count suppressed warning backtraces > kunit: Add test cases for backtrace warning suppression > kunit: Add documentation for warning backtrace suppression API > drm: Suppress intentional warning backtraces in scaling unit tests > net: kunit: Suppress lock warning noise at end of dev_addr_lists tests > x86: Add support for suppressing warning backtraces > arm64: Add support for suppressing warning backtraces > loongarch: Add support for suppressing warning backtraces > parisc: Add support for suppressing warning backtraces > s390: Add support for suppressing warning backtraces > sh: Add support for suppressing warning backtraces > sh: Move defines needed for suppressing warning backtraces > riscv: Add support for suppressing warning backtraces > powerpc: Add support for suppressing warning backtraces Tested-by: Kees Cook <keescook@xxxxxxxxxxxx> (for x86 and um) I was planning to add warning suppression for the "overflow" KUnit tests, but it seems the vmalloc routines aren't calling warn_alloc() any more for impossible sizes. So, I think, no patches needed for lib/overflow_kunit.c, but at the end of the day, I've tested this series is working for me. :P -- Kees Cook
