linux-kernel - Re: [PATCH RFC 3/3] kfence: Make test case compatible with run time set sample interval

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Date:   Mon, 24 Jan 2022 09:25:36 +0100
From:   Marco Elver <elver@...gle.com>
To:     Peng Liu <liupeng256@...wei.com>
Cc:     glider@...gle.com, dvyukov@...gle.com, corbet@....net,
        sumit.semwal@...aro.org, christian.koenig@....com,
        akpm@...ux-foundation.org, kasan-dev@...glegroups.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org
Subject: Re: [PATCH RFC 3/3] kfence: Make test case compatible with run time
 set sample interval

On Mon, 24 Jan 2022 at 03:37, 'Peng Liu' via kasan-dev
<kasan-dev@...glegroups.com> wrote:
>
> The parameter kfence_sample_interval can be set via boot parameter
> and late shell command. However, KFENCE test case just use compile
> time CONFIG_KFENCE_SAMPLE_INTERVAL, this will make KFENCE test case
> not run as user desired. This patch will make KFENCE test case
> compatible with run-time-set sample interval.
>
> Signed-off-by: Peng Liu <liupeng256@...wei.com>
> ---
>  include/linux/kfence.h  | 2 ++
>  mm/kfence/core.c        | 3 ++-
>  mm/kfence/kfence_test.c | 8 ++++----
>  3 files changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/kfence.h b/include/linux/kfence.h
> index bf91b76b87ee..0fc913a7f017 100644
> --- a/include/linux/kfence.h
> +++ b/include/linux/kfence.h
> @@ -19,6 +19,8 @@
>
>  extern bool kfence_enabled;
>  extern unsigned long kfence_num_objects;
> +extern unsigned long kfence_sample_interval;
> +
>  /*
>   * We allocate an even number of pages, as it simplifies calculations to map
>   * address to metadata indices; effectively, the very first page serves as an
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 2301923182b8..e2fcae34cc84 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -50,7 +50,8 @@
>
>  bool kfence_enabled __read_mostly;
>
> -static unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL;
> +unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL;
> +EXPORT_SYMBOL(kfence_sample_interval); /* Export for test modules. */

While it would make some situations more convenient, I've wanted to
avoid exporting a new symbol just for the test. And in most cases it
only makes sense to run the test on a custom debug kernel.

Why do you need this?

Should you really need this, I suggest at least using
EXPORT_SYMBOL_GPL. Should you want it, you can resend this patch
standalone detached from the rest.

Thanks,
-- Marco