linux-kernel - Re: [PATCH 1/3] selftests/resctrl: Fix schemata write error check

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Message-ID: <5c6a2065-6771-ed87-c5ed-843f4e184ff8@linux.intel.com>
Date:   Thu, 24 Aug 2023 15:52:05 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     "Wieczor-Retman, Maciej" <maciej.wieczor-retman@...el.com>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Reinette Chatre <reinette.chatre@...el.com>,
        fenghua.yu@...el.com
Subject: Re: [PATCH 1/3] selftests/resctrl: Fix schemata write error check

Ki,

You're lacking a few people from the To/Cc list. Please see KERNEL 
SELFTEST FRAMEWORK entry in MAINTAINERS.

On Thu, 24 Aug 2023, Wieczor-Retman, Maciej wrote:

> Writing bitmasks to the schemata can fail when the bitmask doesn't
> adhere to some constraints defined by what a particular CPU supports.
> Some example of constraints are max length or being having contiguous

"being having" is not good English.

> bits. The driver should properly return errors when any rule concerning
> bitmask format is broken.
> 
> Resctrl FS returns error codes from fprintf() only when fclose() is
> called.

I wonder if this is actually related to libc doing buffering between 
fprintf() and the actual write() syscall.

> Current error checking scheme allows invalid bitmasks to be
> written into schemata file and the selftest doesn't notice because the
> fclose() error code isn't checked.
> 
> Add error check to the fclose() call.
> 
> Add perror() just after fprintf so a proper error message can be seen.
> 
> Signed-off-by: Wieczor-Retman, Maciej <maciej.wieczor-retman@...el.com>
> ---
>  tools/testing/selftests/resctrl/resctrlfs.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
> index bd36ee206602..a6d0b632cbc6 100644
> --- a/tools/testing/selftests/resctrl/resctrlfs.c
> +++ b/tools/testing/selftests/resctrl/resctrlfs.c
> @@ -532,13 +532,17 @@ int write_schemata(char *ctrlgrp, char *schemata, int cpu_no, char *resctrl_val)
>  	}
>  
>  	if (fprintf(fp, "%s\n", schema) < 0) {
> -		sprintf(reason, "Failed to write schemata in control group");
> +		sprintf(reason, "fprintf() failed with error : %s",
> +			strerror(errno));

These should use snprintf() to make sure the buffer does not overflow. 

>  		fclose(fp);
>  		ret = -1;
>  
>  		goto out;
>  	}
> -	fclose(fp);
> +	ret = fclose(fp);
> +	if (ret)
> +		sprintf(reason, "Failed to write schemata in control group : %s",
> +			strerror(errno));
>  
>  out:
>  	ksft_print_msg("Write schema \"%s\" to resctrl FS%s%s\n",
> 

-- 
 i.