linux-kernel - Re: [PATCH v2 02/24] selftests/resctrl: Check also too low values for CBM bits

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Message-ID: <4bae56e1-9223-7d94-e6da-72504f3d0be3@intel.com>
Date:   Fri, 21 Apr 2023 17:08:21 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        <linux-kselftest@...r.kernel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "Shuah Khan" <shuah@...nel.org>, <linux-kernel@...r.kernel.org>
CC:     Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH v2 02/24] selftests/resctrl: Check also too low values for
 CBM bits

Hi Ilpo,

On 4/18/2023 4:44 AM, Ilpo Järvinen wrote:
> CAT test only validates that the number of CBM bits is not too large
> but it could be too small too.

Could you please elaborate how this scenario could occur?

> Check and return error before starting the CAT test if the number of
> CBM bits is too small.
> 
> Fixes: 09a67934625a ("selftests/resctrl: Don't hard code value of "no_of_bits" variable")

This fix is not clear to me. This commit being fixed already contains
an explicit test that will bail out of no_of_bits <= 0. It is not clear to me
why it is necessary to adding a test for < 1 as a fix for this commit.

> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---
>  tools/testing/selftests/resctrl/cat_test.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> index fb1443f888c4..722c9cd4120d 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -129,7 +129,7 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
>  	if (!n)
>  		n = count_of_bits / 2;
>  
> -	if (n > count_of_bits - 1) {
> +	if (n < 1 || n > count_of_bits - 1) {
>  		ksft_print_msg("Invalid input value for no_of_bits n!\n");
>  		ksft_print_msg("Please enter value in range 1 to %d\n",
>  			       count_of_bits - 1);


Reinette