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

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Date:   Mon, 24 Apr 2023 13:46:41 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Reinette Chatre <reinette.chatre@...el.com>
cc:     linux-kselftest@...r.kernel.org, Fenghua Yu <fenghua.yu@...el.com>,
        Shuah Khan <shuah@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH v2 02/24] selftests/resctrl: Check also too low values
 for CBM bits

On Fri, 21 Apr 2023, Reinette Chatre wrote:

> 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.

Ah, indeed, it's checked on the higher level so this fix is unnecessary.
I missed it entirely while taking this change out from a more complex 
change and even failed to make the connection when I stared at the very if 
<= 0 check not so many days ago.

-- 
 i.


> > 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);