RE: [PATCH v5 4/5] selftests/resctrl: Cleanup properly when an error occurs in CAT test

[Shaopeng Tan (Fujitsu)]

Hi Reinette,

> On 1/10/2023 11:58 PM, Shaopeng Tan wrote:
> > After creating a child process with fork() in CAT test, if there is an
> 
> Please delete the "there is" so that it reads  "if an error occurs"

Thanks.

> > error occurs or a signal such as SIGINT is received, the parent
> > process will be terminated immediately, and therefor the child process
> > will not be killed and also resctrlfs is not unmounted.
> >
> > There is a signal handler registered in CMT/MBM/MBA tests, which kills
> > child process, unmount resctrlfs, cleanups result files, etc., if a
> > signal such as SIGINT is received.
> >
> > Commonize the signal handler registered for CMT/MBM/MBA tests and
> > reuse it in CAT too.
> >
> > To reuse the signal handler, make the child process in CAT wait to be
> > killed by parent process in any case (an error occurred or a signal
> > was received), and when killing child process use global bm_pid
> > instead of local bm_pid.
> >
> > Also, since the MBA/MBA/CMT/CAT are run in order, unregister the
> > signal handler at the end of each test so that the signal handler
> > cannot be inherited by other tests.
> >
> > Signed-off-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxxxxx>
> > ---
> >  tools/testing/selftests/resctrl/cat_test.c    | 26 +++++----
> >  tools/testing/selftests/resctrl/fill_buf.c    | 14 -----
> >  tools/testing/selftests/resctrl/resctrl.h     |  2 +
> >  tools/testing/selftests/resctrl/resctrl_val.c | 56
> > ++++++++++++++-----
> >  4 files changed, 59 insertions(+), 39 deletions(-)
> >
> > diff --git a/tools/testing/selftests/resctrl/cat_test.c
> > b/tools/testing/selftests/resctrl/cat_test.c
> > index 6a8306b0a109..87302b882929 100644
> > --- a/tools/testing/selftests/resctrl/cat_test.c
> > +++ b/tools/testing/selftests/resctrl/cat_test.c
> > @@ -103,7 +103,6 @@ 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;
> >
> >  	cache_size = 0;
> >
> > @@ -181,28 +180,29 @@ 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 {
> > +		ret = signal_handler_register();
> > +		if (ret)
> > +			goto out;
> 
> The "goto" will unregister the signal handler. Is that necessary if the registration
> failed?
> 
> Also, if signal_handler_register() fails then the child will keep running and run
> its test ... would child not then run forever?

A signal handler is needed here, but it is rarely used.
Also, the registration rarely fails.
Therefore, if registration failed, 
just print a warning/info message as follow.
how about this idea?

ksft_print_msg("Failed to register signal handler, signals SIGINT/SIGTERM/SIGHUP will not be handled as expected");

> >  	}
> >
> >  	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);
> >
> >  	if (bm_pid == 0) {
> >  		/* Tell parent that child is ready */
> >  		close(pipefd[0]);
> >  		pipe_message = 1;
> >  		if (write(pipefd[1], &pipe_message, sizeof(pipe_message)) <
> > -		    sizeof(pipe_message)) {
> > -			close(pipefd[1]);
> > +		    sizeof(pipe_message))
> > +			/*
> > +			 * Just print the error message.
> > +			 * Let while(1) run and wait for itself to be killed.
> > +			 */
> >  			perror("# failed signaling parent process");
> > -			return errno;
> > -		}
> >
> >  		close(pipefd[1]);
> >  		while (1)
> > @@ -226,5 +226,7 @@ int cat_perf_miss_val(int cpu_no, int n, char
> *cache_type)
> >  	if (bm_pid)
> >  		umount_resctrlfs();
> >
> > -	return 0;
> > +out:
> > +	ret = signal_handler_unregister();
> > +	return ret;
> 
> Be careful here ... any earlier value of "ret" will be overwritten with the result of
> signal_handler_unregister(). I think the return of
> signal_handler_unregister() can be ignored. There will be an error message if it
> failed.

Thanks for your advice, I will ignore the return of signal_handler_unregister().

> >  }
> > diff --git a/tools/testing/selftests/resctrl/fill_buf.c
> > b/tools/testing/selftests/resctrl/fill_buf.c
> > index 56ccbeae0638..322c6812e15c 100644
> > --- a/tools/testing/selftests/resctrl/fill_buf.c
> > +++ b/tools/testing/selftests/resctrl/fill_buf.c
> > @@ -33,14 +33,6 @@ static void sb(void)  #endif  }
> >
> > -static void ctrl_handler(int signo)
> > -{
> > -	free(startptr);
> > -	printf("\nEnding\n");
> > -	sb();
> > -	exit(EXIT_SUCCESS);
> > -}
> > -
> >  static void cl_flush(void *p)
> >  {
> >  #if defined(__i386) || defined(__x86_64) @@ -198,12 +190,6 @@ int
> > run_fill_buf(unsigned long span, int malloc_and_init_memory,
> >  	unsigned long long cache_size = span;
> >  	int ret;
> >
> > -	/* set up ctrl-c handler */
> > -	if (signal(SIGINT, ctrl_handler) == SIG_ERR)
> > -		printf("Failed to catch SIGINT!\n");
> > -	if (signal(SIGHUP, ctrl_handler) == SIG_ERR)
> > -		printf("Failed to catch SIGHUP!\n");
> > -
> >  	ret = fill_cache(cache_size, malloc_and_init_memory, memflush, op,
> >  			 resctrl_val);
> >  	if (ret) {
> > diff --git a/tools/testing/selftests/resctrl/resctrl.h
> > b/tools/testing/selftests/resctrl/resctrl.h
> > index f0ded31fb3c7..14a5e21497e1 100644
> > --- a/tools/testing/selftests/resctrl/resctrl.h
> > +++ b/tools/testing/selftests/resctrl/resctrl.h
> > @@ -107,6 +107,8 @@ void mba_test_cleanup(void);  int
> > get_cbm_mask(char *cache_type, char *cbm_mask);  int
> > get_cache_size(int cpu_no, char *cache_type, unsigned long
> > *cache_size);  void ctrlc_handler(int signum, siginfo_t *info, void
> > *ptr);
> > +int signal_handler_register(void);
> > +int signal_handler_unregister(void);
> >  int cat_val(struct resctrl_val_param *param);  void
> > cat_test_cleanup(void);  int cat_perf_miss_val(int cpu_no, int
> > no_of_bits, char *cache_type); diff --git
> > a/tools/testing/selftests/resctrl/resctrl_val.c
> > b/tools/testing/selftests/resctrl/resctrl_val.c
> > index 6948843bf995..91a3cf8b308b 100644
> > --- a/tools/testing/selftests/resctrl/resctrl_val.c
> > +++ b/tools/testing/selftests/resctrl/resctrl_val.c
> > @@ -476,6 +476,46 @@ void ctrlc_handler(int signum, siginfo_t *info, void
> *ptr)
> >  	exit(EXIT_SUCCESS);
> >  }
> >
> > +struct sigaction sigact;
> > +
> > +/*
> > + * Register CTRL-C handler for parent, as it has to kill
> > + * child process before exiting
> > + */
> > +int signal_handler_register(void)
> > +{
> > +	int ret = 0;
> > +	struct sigaction sigact;
> 
> Why is there a global sigact as well as a local sigact?
> 
> Also, please do keep using reverse fir-tree format.

I was going to use local sigact.
I will delete global sigact and keep using reverse fir-tree format. 
+	struct sigaction sigact;
+	int ret = 0;

> > +
> > +	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");
> > +		ret = errno;
> 
> I understand that you copied from the original code here but I do think there is
> an issue here in that errno is undefined after a library call. perror() will print
> errno message so keeping it (errno) around may not be useful. Please do keep
> the custom of returning negative value as error though. I think just returning -1
> would work.

Thanks for your advice. I will return -1 here.

> > +	}
> > +	return ret;
> > +}
> > +
> > +/* reset signal handler to SIG_DFL. */ int
> > +signal_handler_unregister(void) {
> > +	int ret = 0;
> > +	struct sigaction sigact;
> > +
> > +	sigact.sa_handler = SIG_DFL;
> > +	sigemptyset(&sigact.sa_mask);
> > +	if (sigaction(SIGINT, &sigact, NULL) ||
> > +	    sigaction(SIGTERM, &sigact, NULL) ||
> > +	    sigaction(SIGHUP, &sigact, NULL)) {
> > +		perror("# sigaction");
> > +		ret = errno;
> 
> Same comment about errno and returning -1 on failure.

I will return -1 here.

> > +	}
> > +	return ret;
> > +}
> > +
> >  /*
> >   * print_results_bw:	the memory bandwidth results are stored in a file
> >   * @filename:		file that stores the results
> > @@ -671,20 +711,9 @@ int resctrl_val(char **benchmark_cmd, struct
> > resctrl_val_param *param)
> >
> >  	ksft_print_msg("Benchmark PID: %d\n", bm_pid);
> >
> > -	/*
> > -	 * Register CTRL-C handler for parent, as it has to kill benchmark
> > -	 * 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");
> > -		ret = errno;
> > +	ret = signal_handler_register();
> > +	if (ret)
> >  		goto out;
> > -	}
> >
> >  	value.sival_ptr = benchmark_cmd;
> >
> > @@ -764,6 +793,7 @@ int resctrl_val(char **benchmark_cmd, struct
> > resctrl_val_param *param)
> >  out:
> >  	kill(bm_pid, SIGKILL);
> >  	umount_resctrlfs();
> > +	ret = signal_handler_unregister();
> >
> >  	return ret;
> 
> Same here ... any earlier value of ret will be overwritten with result of
> signal_handler_unregister().

I will ignore the return of signal_handler_unregister().

Best regards,
Shaopeng TAN