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References: <20240319104857.70783-1-mic@digikod.net> <20240319104857.70783-5-mic@digikod.net>
In-Reply-To: <20240319104857.70783-5-mic@digikod.net>
From: David Gow <davidgow@google.com>
Date: Sat, 23 Mar 2024 15:37:21 +0800
Message-ID: <CABVgOSksVq5_AeObEBZFAezZpiQ41C7ZHWEtRBR_1d2UQQYXbw@mail.gmail.com>
Subject: Re: [PATCH v3 4/7] kunit: Handle test faults
To: =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= <mic@digikod.net>
Cc: Brendan Higgins <brendanhiggins@google.com>, Rae Moar <rmoar@google.com>, 
	Shuah Khan <skhan@linuxfoundation.org>, Alan Maguire <alan.maguire@oracle.com>, 
	Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>, 
	"H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>, 
	James Morris <jamorris@linux.microsoft.com>, Kees Cook <keescook@chromium.org>, 
	Luis Chamberlain <mcgrof@kernel.org>, 
	"Madhavan T . Venkataraman" <madvenka@linux.microsoft.com>, Marco Pagani <marpagan@redhat.com>, 
	Paolo Bonzini <pbonzini@redhat.com>, Sean Christopherson <seanjc@google.com>, Stephen Boyd <sboyd@kernel.org>, 
	Thara Gopinath <tgopinath@microsoft.com>, Thomas Gleixner <tglx@linutronix.de>, 
	Vitaly Kuznetsov <vkuznets@redhat.com>, Wanpeng Li <wanpengli@tencent.com>, 
	Zahra Tarkhani <ztarkhani@microsoft.com>, kvm@vger.kernel.org, 
	linux-hardening@vger.kernel.org, linux-hyperv@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, 
	linux-um@lists.infradead.org, x86@kernel.org
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On Tue, 19 Mar 2024 at 18:49, Micka=C3=ABl Sala=C3=BCn <mic@digikod.net> wr=
ote:
>
> 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 -EINTR 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@google.com>
> Cc: Shuah Khan <skhan@linuxfoundation.org>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: David Gow <davidgow@google.com>
> Tested-by: Rae Moar <rmoar@google.com>
> Signed-off-by: Micka=C3=ABl Sala=C3=BCn <mic@digikod.net>
> Link: https://lore.kernel.org/r/20240319104857.70783-5-mic@digikod.net
> ---
>
> Changes since v2:
> * s/-EFAULT/-EINTR/ in commit message as spotted by Rae.
> * Add a comment explaining vfork_done as suggested by David.
> * Add David's Reviewed-by.
> * Add Rae's Tested-by.
>
> Changes since v1:
> * Add Kees's Reviewed-by.
> ---
>  include/kunit/try-catch.h |  3 ---
>  lib/kunit/try-catch.c     | 19 ++++++++++++-------
>  2 files changed, 12 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 mig=
ht fail.
>   * @test: The test case that is currently being executed.
> - * @try_completion: Completion that the control thread waits on while te=
st 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..7a3910dd78a6 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 =3D -EFAULT;
> -       kthread_complete_and_exit(try_catch->try_completion, -EFAULT);
> +       kthread_exit(0);

It turns out kthread_exit() is not exported, so this doesn't work if
KUnit is built as a module.

I think the options we have are:
- Add EXPORT_SYMBOL(kthread_exit).
- Keep using out own completion, and kthread_complete_and_exit()
- try_get_module() before spawning the thread, and use
module_put_and_kthread_exit().

I think all of these would be okay, but I could've missed something.

-- David

>  }
>  EXPORT_SYMBOL_GPL(kunit_try_catch_throw);
>
> @@ -26,9 +26,12 @@ static int kunit_generic_run_threadfn_adapter(void *da=
ta)
>  {
>         struct kunit_try_catch *try_catch =3D data;
>
> +       try_catch->try_result =3D -EINTR;
>         try_catch->try(try_catch->context);
> +       if (try_catch->try_result =3D=3D -EINTR)
> +               try_catch->try_result =3D 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 *contex=
t)
>  {
> -       DECLARE_COMPLETION_ONSTACK(try_completion);
>         struct kunit *test =3D try_catch->test;
>         struct task_struct *task_struct;
>         int exit_code, time_remaining;
>
>         try_catch->context =3D context;
> -       try_catch->try_completion =3D &try_completion;
>         try_catch->try_result =3D 0;
>         task_struct =3D kthread_create(kunit_generic_run_threadfn_adapter=
,
>                                      try_catch, "kunit_try_catch_thread")=
;
> @@ -75,8 +76,12 @@ void kunit_try_catch_run(struct kunit_try_catch *try_c=
atch, void *context)
>         }
>         get_task_struct(task_struct);
>         wake_up_process(task_struct);
> -
> -       time_remaining =3D wait_for_completion_timeout(&try_completion,
> +       /*
> +        * As for a vfork(2), task_struct->vfork_done (pointing to the
> +        * underlying kthread->exited) can be used to wait for the end of=
 a
> +        * kernel thread.
> +        */
> +       time_remaining =3D wait_for_completion_timeout(task_struct->vfork=
_done,
>                                                      kunit_test_timeout()=
);
>         if (time_remaining =3D=3D 0) {
>                 try_catch->try_result =3D -ETIMEDOUT;
> @@ -92,7 +97,7 @@ void kunit_try_catch_run(struct kunit_try_catch *try_ca=
tch, void *context)
>         if (exit_code =3D=3D -EFAULT)
>                 try_catch->try_result =3D 0;
>         else if (exit_code =3D=3D -EINTR)
> -               kunit_err(test, "wake_up_process() was never called\n");
> +               kunit_err(test, "try faulted\n");
>         else if (exit_code =3D=3D -ETIMEDOUT)
>                 kunit_err(test, "try timed out\n");
>         else if (exit_code)
> --
> 2.44.0
>

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