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Date: Mon, 23 Jan 2023 04:22:03 +0000
From: "Shaopeng Tan (Fujitsu)" <tan.shaopeng@...itsu.com>
To: 'Reinette Chatre' <reinette.chatre@...el.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>
Subject: RE: [PATCH v5 4/5] selftests/resctrl: Cleanup properly when an error
occurs in CAT test
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@...fujitsu.com>
> > ---
> > 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(¶m);
> > - if (ret)
> > - return ret;
> > -
> > - ret = check_results(¶m);
> > - if (ret)
> > - return ret;
> > + if (ret == 0)
> > + ret = check_results(¶m);
> >
> > 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
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