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

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Date:   Wed, 23 Nov 2022 09:48:14 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     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>,
        "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 11/16/2022 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
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.

Reinette