linux-kernel - Re: [PATCH v2 3/3] mm: slub: test: Use the kunit_get_current

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Date:   Tue, 25 Oct 2022 11:07:03 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     David Gow <davidgow@...gle.com>,
        Brendan Higgins <brendan.higgins@...ux.dev>,
        Daniel Latypov <dlatypov@...gle.com>,
        Shuah Khan <skhan@...uxfoundation.org>
Cc:     kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        Oliver Glitta <glittao@...il.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 3/3] mm: slub: test: Use the kunit_get_current_test()
 function

On 10/25/22 09:19, David Gow wrote:
> Use the newly-added function kunit_get_current_test() instead of
> accessing current->kunit_test directly. This function uses a static key
> to return more quickly when KUnit is enabled, but no tests are actively
> running. There should therefore be a negligible performance impact to
> enabling the slub KUnit tests.
> 
> Other than the performance improvement, this should be a no-op.
> 
> Cc: Oliver Glitta <glittao@...il.com>
> Cc: Hyeonggon Yoo <42.hyeyoo@...il.com>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: David Gow <davidgow@...gle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
> 
> This is intended as an example use of the new function. Other users
> (such as KASAN) will be updated separately, as there would otherwise be
> conflicts.
> 
> Assuming there are no objections, we'll take this whole series via the
> kselftest/kunit tree.

OK, please do.

Some possible improvements below:

> There was no v1 of this patch. v1 of the series can be found here:
> https://lore.kernel.org/linux-kselftest/20221021072854.333010-1-davidgow@google.com/T/#u
> 
> ---
>  lib/slub_kunit.c | 1 +
>  mm/slub.c        | 5 +++--
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/slub_kunit.c b/lib/slub_kunit.c
> index 7a0564d7cb7a..8fd19c8301ad 100644
> --- a/lib/slub_kunit.c
> +++ b/lib/slub_kunit.c
> @@ -1,5 +1,6 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include <kunit/test.h>
> +#include <kunit/test-bug.h>
>  #include <linux/mm.h>
>  #include <linux/slab.h>
>  #include <linux/module.h>
> diff --git a/mm/slub.c b/mm/slub.c
> index 157527d7101b..15d10d250ef2 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -39,6 +39,7 @@
>  #include <linux/memcontrol.h>
>  #include <linux/random.h>
>  #include <kunit/test.h>
> +#include <kunit/test-bug.h>
>  #include <linux/sort.h>
>  
>  #include <linux/debugfs.h>
> @@ -603,10 +604,10 @@ static bool slab_add_kunit_errors(void)
>  {
>  	struct kunit_resource *resource;
>  
> -	if (likely(!current->kunit_test))
> +	if (likely(!kunit_get_current_test()))

Given that kunit_get_current_test() is basically an inline
!static_branch_unlikely(), IMHO the likely() here doesn't add anything and
could be removed?

>  		return false;
>  
> -	resource = kunit_find_named_resource(current->kunit_test, "slab_errors");
> +	resource = kunit_find_named_resource(kunit_get_current_test(), "slab_errors");

We just passed kunit_get_current_test() above so maybe we could just keep
using current->kunit_test here? Seems unnecessary adding another jump label.

>  	if (!resource)
>  		return false;
>