linux-kernel - Re: [PATCH v4 2/3] kunit: Use the static key when retrieving the current test

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Message-ID: <202212011654.9BB14785@keescook>
Date:   Thu, 1 Dec 2022 16:54:35 -0800
From:   Kees Cook <keescook@...omium.org>
To:     David Gow <davidgow@...gle.com>
Cc:     Brendan Higgins <brendan.higgins@...ux.dev>,
        Daniel Latypov <dlatypov@...gle.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-mm@...ck.org, Jonathan Corbet <corbet@....net>,
        Sadiya Kazi <sadiyakazi@...gle.com>
Subject: Re: [PATCH v4 2/3] kunit: Use the static key when retrieving the
 current test

On Fri, Nov 25, 2022 at 04:43:05PM +0800, David Gow wrote:
> In order to detect if a KUnit test is running, and to access its
> context, the 'kunit_test' member of the current task_struct is used.
> Usually, this is accessed directly or via the kunit_fail_current_task()
> function.
> 
> In order to speed up the case where no test is running, add a wrapper,
> kunit_get_current_test(), which uses the static key to fail early.
> Equally, Speed up kunit_fail_current_test() by using the static key.
> 
> This should make it convenient for code to call this
> unconditionally in fakes or error paths, without worrying that this will
> slow the code down significantly.
> 
> If CONFIG_KUNIT=n (or m), this compiles away to nothing. If
> CONFIG_KUNIT=y, it will compile down to a NOP (on most architectures) if
> no KUnit test is currently running.
> 
> Note that kunit_get_current_test() does not work if KUnit is built as a
> module. This mirrors the existing restriction on kunit_fail_current_test().
> 
> Note that the definition of kunit_fail_current_test() still wraps an
> empty, inline function if KUnit is not built-in. This is to ensure that
> the printf format string __attribute__ will still work.
> 
> Also update the documentation to suggest users use the new
> kunit_get_current_test() function, update the example, and to describe
> the behaviour when KUnit is disabled better.
> 
> Cc: Jonathan Corbet <corbet@....net>
> Cc: Sadiya Kazi <sadiyakazi@...gle.com>
> Signed-off-by: David Gow <davidgow@...gle.com>

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

-- 
Kees Cook