linux-kernel - Re: [PATCH v4 4/5] selftests/resctrl: Cleanup properly when an error occurs in CAT test

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Message-ID: <ba5a9ef2-b4ca-5c90-cc03-2296586455a6@intel.com>
Date:   Mon, 28 Nov 2022 09:11:15 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     "Shaopeng Tan (Fujitsu)" <tan.shaopeng@...itsu.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Shuah Khan <shuah@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Shuah Khan" <skhan@...uxfoundation.org>
Subject: Re: [PATCH v4 4/5] selftests/resctrl: Cleanup properly when an error
 occurs in CAT test

Hi Shaopeng,

On 11/24/2022 12:17 AM, Shaopeng Tan (Fujitsu) wrote:
> Hi Reinette,
> 
>> On 11/16/2022 5:05 PM, 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. if an error occurs in parent
>>> process. To use ctrlc_handler() of other tests to kill child
>>> process(bm_pid), using global bm_pid instead of local bm_pid.
>>>
>>> Wait for child process to be killed if an error occurs in child process.
>>>
>>> Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>
>>> Signed-off-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
>>> ---
>>>  tools/testing/selftests/resctrl/cat_test.c | 30
>> ++++++++++++++--------
>>>  1 file changed, 20 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/tools/testing/selftests/resctrl/cat_test.c
>> b/tools/testing/selftests/resctrl/cat_test.c
>>> index 6a8306b0a109..1f8f5cf94e95 100644
>>> --- a/tools/testing/selftests/resctrl/cat_test.c
>>> +++ b/tools/testing/selftests/resctrl/cat_test.c
>>> @@ -100,10 +100,10 @@ void cat_test_cleanup(void)
>>>
>>>  int cat_perf_miss_val(int cpu_no, int n, char *cache_type)
>>>  {
>>> +	struct sigaction sigact;
>>>  	unsigned long l_mask, l_mask_1;
>>>  	int ret, pipefd[2], sibling_cpu_no;
>>>  	char pipe_message;
>>> -	pid_t bm_pid;
>>>
>>>  	cache_size = 0;
>>>
>>> @@ -181,17 +181,25 @@ 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 {
>>> +		/*
>>> +		 * Register CTRL-C handler for parent, as it has to kill
>>> +		 * child process before exiting
>>> +		 */
>>> +		sigact.sa_sigaction = ctrlc_handler;
>>> +		sigemptyset(&sigact.sa_mask);
>>> +		sigact.sa_flags = SA_SIGINFO;
>>> +		if (sigaction(SIGINT, &sigact, NULL) ||
>>> +		    sigaction(SIGTERM, &sigact, NULL) ||
>>> +		    sigaction(SIGHUP, &sigact, NULL))
>>> +			perror("# sigaction");
>>
>> Why keep going at this point?
>>
>> I tried this change but I was not able to trigger ctrlc_handler(). It
> 
> I tested this change using kselftest framework,
> In this case, the timeout command sent a SIGTERM signal,
> and then ctrlc_handler() was triggered.
> Since the handling of SIGINT and SIGHUP signals is overridden in run_fill_buf(), 
> ctrl_handler() may be called if ctrl-c is received.

I tested this by running "resctrl_tests -t cat" and when doing so
this change does not behave as described.


>> seems that the handler is changed soon after (see cat_val()->run_fill_buf())
>> and ctrl_handler() (note the subtle name difference) is run instead when
>> a SIGINT is received. The value of ctrl_handler() is not clear to me though,
>> and it could even be argued that it is broken because it starts with
>> free(startptr) and startptr would likely already be free'd at this point
>> without resetting its value to NULL.
>>
>> From what I understand ctrl_handler() and its installation from
>> run_fill_buf() could be removed so that it does not override what is being
>> done with this change. Otherwise, from what I can tell, this new handler
>> will never run.
> 
> I think removing ctrl_handler() is fine. 
> In CAT test, it overrides ctrlc_handler().
> In other tests(CMT,MBA,MBM), the child process used ctrl_handler() to cleanup itself,

Is that explicit cleanup required? All I can see is free(startptr) and that pointer
would usually be invalid as I mentioned earlier. If the process crashes while
running fill_cache() and thus not get a chance to run free(startptr) then
the OS would release the memory, no?

> but the parent process cleanup the child process with ctrlc_handler() properly.
> Also, avoid using signal().
>  fill_buf.c：run_fill_buf()
>  201         /* set up ctrl-c handler */
>  202         if (signal(SIGINT, ctrl_handler) == SIG_ERR)
>  203                 printf("Failed to catch SIGINT!\n");
> 
> I removed ctrl_handler() and ran resctrl_tests with and without the kselftest framework.
> There is no problem.

Thank you. I only used the CAT test when I found the issue.

Reinette