linux-kernel - Re: [PATCH v3 4/5] selftests/resctrl: Cleanup properly when an error occurs in CAT test

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Date:   Mon, 7 Nov 2022 14:31:34 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Shuah Khan <skhan@...uxfoundation.org>,
        Shaopeng Tan <tan.shaopeng@...fujitsu.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Shuah Khan <shuah@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v3 4/5] selftests/resctrl: Cleanup properly when an error
 occurs in CAT test

Hi Shaopeng and Shuah,

On 11/2/2022 2:41 AM, Shuah Khan wrote:
> On 11/1/22 03:43, Shaopeng Tan wrote:
>> After creating a child process with fork() in CAT test, if there is
>> an error occurs or such as a SIGINT signal is received, the parent
>> process will be terminated immediately, but the child process will not
>> be killed and also umount_resctrlfs() will not be called.
>>
>> Add a signal handler like other tests to kill child process, umount
>> resctrlfs, cleanup result files, etc. when an error occurs.
>>
>> Signed-off-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
>> ---
>>   tools/testing/selftests/resctrl/cat_test.c | 28 +++++++++++++++-------
>>   1 file changed, 19 insertions(+), 9 deletions(-)
>>
>> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
>> index 6a8306b0a109..5f81817f4366 100644
>> --- a/tools/testing/selftests/resctrl/cat_test.c
>> +++ b/tools/testing/selftests/resctrl/cat_test.c
>> @@ -98,12 +98,21 @@ void cat_test_cleanup(void)
>>       remove(RESULT_FILE_NAME2);
>>   }
>>   +static void ctrl_handler(int signo)
>> +{
>> +    kill(bm_pid, SIGKILL);
>> +    umount_resctrlfs();
>> +    tests_cleanup();
>> +    ksft_print_msg("Ending\n\n");
> 
> Is there a reason to print this message? Remove it unless it serves
> a purpose.

This function appears to be a duplicate of existing
resctrl_val.c:ctrlc_handler(). Could the duplication be avoided
instead of refining the copy?

> 
>> +
>> +    exit(EXIT_SUCCESS);
>> +}
>> +
>>   int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
>>   {
>>       unsigned long l_mask, l_mask_1;
>>       int ret, pipefd[2], sibling_cpu_no;
>>       char pipe_message;
>> -    pid_t bm_pid;
> 
> Odd. bm_pid is used below - why remove it here?

There is a global bm_pid in resctrl_val.c that is made available
via extern in resctrl.h. This is what causes this code to still
compile but I would also like to learn why moving to that is
desired as a change here. I expect such a big change to get a
mention in the commit message.

> 
>>         cache_size = 0;
>>   @@ -181,17 +190,19 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
>>           strcpy(param.filename, RESULT_FILE_NAME1);
>>           param.num_of_runs = 0;
>>           param.cpu_no = sibling_cpu_no;
>> +    } else {
>> +        /* set up ctrl-c handler */
>> +        if (signal(SIGINT, ctrl_handler) == SIG_ERR ||
>> +            signal(SIGHUP, ctrl_handler) == SIG_ERR ||
>> +            signal(SIGTERM, ctrl_handler) == SIG_ERR)
>> +            printf("Failed to catch SIGNAL!\n");
> 
> Is perror() more appropriate here?

Should we be using signal() at all? "man signal" reads:
"WARNING: the behavior of signal() varies across UNIX versions,
and has also varied historically across different versions of Linux.
Avoid its use: use sigaction(2) instead."

"Failed to catch SIGNAL" also seems unclear to me. This is
where a signal handler is set up, the signal for which the handler
is installed has not arrived.


> 
>>       }
>>         remove(param.filename);
>>         ret = cat_val(&param);
>> -    if (ret)
>> -        return ret;
>> -
>> -    ret = check_results(&param);
>> -    if (ret)
>> -        return ret;
>> +    if (ret == 0)
>> +        ret = check_results(&param);
> 
> Why not use a goto in error case to do umount_resctrlfs() instead of changing
> the conditionals?

My understanding is the code that follows is needed to
synchronize the exits between the parent and child. It is the parent
that will run umount_resctrlfs() and it should only do so
after the child is done. A goto by the parent may thus cause
umount_resctrlfs() to be run while the child still relies on it while
a goto by the child may cause the parent not to receive the message
that the child is complete.

Reinette