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Date:   Thu, 1 Dec 2022 16:53:06 -0800
From:   Kees Cook <keescook@chromium.org>
To:     David Gow <davidgow@google.com>
Cc:     Brendan Higgins <brendan.higgins@linux.dev>,
        Daniel Latypov <dlatypov@google.com>,
        Shuah Khan <skhan@linuxfoundation.org>,
        kunit-dev@googlegroups.com, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH v4 1/3] kunit: Provide a static key to check if KUnit is
 actively running tests
Message-ID: <202212011652.4E8CB40@keescook>
References: <20221125084306.1063074-1-davidgow@google.com>
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On Fri, Nov 25, 2022 at 04:43:04PM +0800, David Gow wrote:
> KUnit does a few expensive things when enabled. This hasn't been a
> problem because KUnit was only enabled on test kernels, but with a few
> people enabling (but not _using_) KUnit on production systems, we need a
> runtime way of handling this.
> 
> Provide a 'kunit_running' static key (defaulting to false), which allows
> us to hide any KUnit code behind a static branch. This should reduce the
> performance impact (on other code) of having KUnit enabled to a single
> NOP when no tests are running.
> 
> Note that, while it looks unintuitive, tests always run entirely within
> __kunit_test_suites_init(), so it's safe to decrement the static key at
> the end of this function, rather than in __kunit_test_suites_exit(),
> which is only there to clean up results in debugfs.
> 
> Signed-off-by: David Gow <davidgow@google.com>
> Reviewed-by: Daniel Latypov <dlatypov@google.com>
> ---
> This should be a no-op (other than a possible performance improvement)
> functionality-wise, and lays the groundwork for a more optimised static
> stub implementation.
> 
> The remaining patches in the series add a kunit_get_current_test()
> function which is a more friendly and performant wrapper around
> current->kunit_test, and use this in the slub test. They also improve
> the documentation a bit.
> 
> If there are no objections, we'll take the whole series via the KUnit
> tree.
> 
> Changes since v3:
> https://lore.kernel.org/linux-kselftest/20221119081252.3864249-1-davidgow@google.com/
> - Use DECLARE_STATIC_KEY_FALSE() -- thanks Daniel!
> 
> No changes since v2:
> https://lore.kernel.org/all/20221025071907.1251820-1-davidgow@google.com/
> 
> Changes since v1:
> https://lore.kernel.org/linux-kselftest/20221021072854.333010-1-davidgow@google.com/
> - No changes in this patch.
> - Patch 2/3 is reworked, patch 3/3 is new.
> 
> ---
>  include/kunit/test.h | 4 ++++
>  lib/kunit/test.c     | 6 ++++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/include/kunit/test.h b/include/kunit/test.h
> index 4666a4d199ea..87ea90576b50 100644
> --- a/include/kunit/test.h
> +++ b/include/kunit/test.h
> @@ -16,6 +16,7 @@
>  #include <linux/container_of.h>
>  #include <linux/err.h>
>  #include <linux/init.h>
> +#include <linux/jump_label.h>
>  #include <linux/kconfig.h>
>  #include <linux/kref.h>
>  #include <linux/list.h>
> @@ -27,6 +28,9 @@
>  
>  #include <asm/rwonce.h>
>  
> +/* Static key: true if any KUnit tests are currently running */
> +DECLARE_STATIC_KEY_FALSE(kunit_running);
> +
>  struct kunit;
>  
>  /* Size of log associated with test. */
> diff --git a/lib/kunit/test.c b/lib/kunit/test.c
> index 1c9d8d962d67..87a5d795843b 100644
> --- a/lib/kunit/test.c
> +++ b/lib/kunit/test.c
> @@ -20,6 +20,8 @@
>  #include "string-stream.h"
>  #include "try-catch-impl.h"
>  
> +DEFINE_STATIC_KEY_FALSE(kunit_running);
> +
>  #if IS_BUILTIN(CONFIG_KUNIT)
>  /*
>   * Fail the current test and print an error message to the log.
> @@ -615,10 +617,14 @@ int __kunit_test_suites_init(struct kunit_suite * const * const suites, int num_
>  		return 0;
>  	}
>  
> +	static_branch_inc(&kunit_running);

Is it expected there will be multiple tests running? (I was expecting
"static_branch_enable").

> +
>  	for (i = 0; i < num_suites; i++) {
>  		kunit_init_suite(suites[i]);
>  		kunit_run_tests(suites[i]);
>  	}
> +
> +	static_branch_dec(&kunit_running);
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(__kunit_test_suites_init);
> -- 
> 2.38.1.584.g0f3c55d4c2-goog
> 

Regardless:

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook