[PATCH v2 4/7] kunit: Handle test faults

[David Gow]

On Sat, 2 Mar 2024 at 03:40, Mickaël Salaün <mic at digikod.net> wrote:
>
> Previously, when a kernel test thread crashed (e.g. NULL pointer
> dereference, general protection fault), the KUnit test hanged for 30
> seconds and exited with a timeout error.
>
> Fix this issue by waiting on task_struct->vfork_done instead of the
> custom kunit_try_catch.try_completion, and track the execution state by
> initially setting try_result with -EFAULT and only setting it to 0 if
> the test passed.
>
> Fix kunit_generic_run_threadfn_adapter() signature by returning 0
> instead of calling kthread_complete_and_exit().  Because thread's exit
> code is never checked, always set it to 0 to make it clear.
>
> Fix the -EINTR error message, which couldn't be reached until now.
>
> This is tested with a following patch.
>
> Cc: Brendan Higgins <brendanhiggins at google.com>
> Cc: David Gow <davidgow at google.com>
> Cc: Rae Moar <rmoar at google.com>
> Cc: Shuah Khan <skhan at linuxfoundation.org>
> Reviewed-by: Kees Cook <keescook at chromium.org>
> Signed-off-by: Mickaël Salaün <mic at digikod.net>
> Link: https://lore.kernel.org/r/20240301194037.532117-5-mic@digikod.net
> ---

This works fine here, and looks good.

The use of task_struct->vfork_done is a bit confusing, as there's no
documentation (that I could find) about what vfork_done means for
kthreads. From the code, it looks to just be a copy of
kthread->exited, which is much more obvious a name.

Would it make sense to either (a) replace this with a call to
to_kthread(), and kthread->exited, or (b) add a comment explaining
what vfork_done means here. kthread_stop() itself is using
to_kthread() and kthread->exited -- even though task_struct is also
there -- so I'd feel a bit more comfortable with that option.

Otherwise,
Reviewed-by: David Gow <davidgow at google.com>

Cheers,
-- David

>
> Changes since v1:
> * Added Kees's Reviewed-by.
> ---
>  include/kunit/try-catch.h |  3 ---
>  lib/kunit/try-catch.c     | 14 +++++++-------
>  2 files changed, 7 insertions(+), 10 deletions(-)
>
> diff --git a/include/kunit/try-catch.h b/include/kunit/try-catch.h
> index c507dd43119d..7c966a1adbd3 100644
> --- a/include/kunit/try-catch.h
> +++ b/include/kunit/try-catch.h
> @@ -14,13 +14,11 @@
>
>  typedef void (*kunit_try_catch_func_t)(void *);
>
> -struct completion;
>  struct kunit;
>
>  /**
>   * struct kunit_try_catch - provides a generic way to run code which might fail.
>   * @test: The test case that is currently being executed.
> - * @try_completion: Completion that the control thread waits on while test runs.
>   * @try_result: Contains any errno obtained while running test case.
>   * @try: The function, the test case, to attempt to run.
>   * @catch: The function called if @try bails out.
> @@ -46,7 +44,6 @@ struct kunit;
>  struct kunit_try_catch {
>         /* private: internal use only. */
>         struct kunit *test;
> -       struct completion *try_completion;
>         int try_result;
>         kunit_try_catch_func_t try;
>         kunit_try_catch_func_t catch;
> diff --git a/lib/kunit/try-catch.c b/lib/kunit/try-catch.c
> index cab8b24b5d5a..c6ee4db0b3bd 100644
> --- a/lib/kunit/try-catch.c
> +++ b/lib/kunit/try-catch.c
> @@ -18,7 +18,7 @@
>  void __noreturn kunit_try_catch_throw(struct kunit_try_catch *try_catch)
>  {
>         try_catch->try_result = -EFAULT;
> -       kthread_complete_and_exit(try_catch->try_completion, -EFAULT);
> +       kthread_exit(0);
>  }
>  EXPORT_SYMBOL_GPL(kunit_try_catch_throw);
>
> @@ -26,9 +26,12 @@ static int kunit_generic_run_threadfn_adapter(void *data)
>  {
>         struct kunit_try_catch *try_catch = data;
>
> +       try_catch->try_result = -EINTR;
>         try_catch->try(try_catch->context);
> +       if (try_catch->try_result == -EINTR)
> +               try_catch->try_result = 0;
>
> -       kthread_complete_and_exit(try_catch->try_completion, 0);
> +       return 0;
>  }
>
>  static unsigned long kunit_test_timeout(void)
> @@ -58,13 +61,11 @@ static unsigned long kunit_test_timeout(void)
>
>  void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
>  {
> -       DECLARE_COMPLETION_ONSTACK(try_completion);
>         struct kunit *test = try_catch->test;
>         struct task_struct *task_struct;
>         int exit_code, time_remaining;
>
>         try_catch->context = context;
> -       try_catch->try_completion = &try_completion;
>         try_catch->try_result = 0;
>         task_struct = kthread_create(kunit_generic_run_threadfn_adapter,
>                                      try_catch, "kunit_try_catch_thread");
> @@ -75,8 +76,7 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
>         }
>         get_task_struct(task_struct);
>         wake_up_process(task_struct);
> -
> -       time_remaining = wait_for_completion_timeout(&try_completion,
> +       time_remaining = wait_for_completion_timeout(task_struct->vfork_done,
>                                                      kunit_test_timeout());
>         if (time_remaining == 0) {
>                 try_catch->try_result = -ETIMEDOUT;
> @@ -92,7 +92,7 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
>         if (exit_code == -EFAULT)
>                 try_catch->try_result = 0;
>         else if (exit_code == -EINTR)
> -               kunit_err(test, "wake_up_process() was never called\n");
> +               kunit_err(test, "try faulted\n");
>         else if (exit_code == -ETIMEDOUT)
>                 kunit_err(test, "try timed out\n");
>         else if (exit_code)
> --
> 2.44.0
>
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