On Tue, Jul 23, 2019 at 10:39:07AM -0700, Suren Baghdasaryan wrote:
> This adds testing for polling on pidfd of a process being killed. Test runs
> 10000 iterations by default to stress test pidfd polling functionality.
> It accepts an optional command-line parameter to override the number or
> iterations to run.
> Specifically, it tests for:
> - pidfd_open on a child process succeeds
> - pidfd_send_signal on a child process succeeds
> - polling on pidfd succeeds and returns exactly one event
> - returned event is POLLIN
> - event is received within 3 secs of the process being killed
>
> 10000 iterations was chosen because of the race condition being tested
> which is not consistently reproducible but usually is revealed after less
> than 2000 iterations.
> Reveals race fixed by commit b191d6491be6 ("pidfd: fix a poll race when setting exit_state")
Thanks for upstreaming the stress-tester. A few comments below.
>
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> ---
> tools/testing/selftests/pidfd/.gitignore | 1 +
> tools/testing/selftests/pidfd/Makefile | 2 +-
> .../testing/selftests/pidfd/pidfd_poll_test.c | 137 ++++++++++++++++++
> 3 files changed, 139 insertions(+), 1 deletion(-)
> create mode 100644 tools/testing/selftests/pidfd/pidfd_poll_test.c
>
> diff --git a/tools/testing/selftests/pidfd/.gitignore b/tools/testing/selftests/pidfd/.gitignore
> index 16d84d117bc0..a67896347d34 100644
> --- a/tools/testing/selftests/pidfd/.gitignore
> +++ b/tools/testing/selftests/pidfd/.gitignore
> @@ -1,2 +1,3 @@
> pidfd_open_test
> +pidfd_poll_test
> pidfd_test
> diff --git a/tools/testing/selftests/pidfd/Makefile b/tools/testing/selftests/pidfd/Makefile
> index 720b2d884b3c..ed58b7108d18 100644
> --- a/tools/testing/selftests/pidfd/Makefile
> +++ b/tools/testing/selftests/pidfd/Makefile
> @@ -1,7 +1,7 @@
> # SPDX-License-Identifier: GPL-2.0-only
> CFLAGS += -g -I../../../../usr/include/ -lpthread
>
> -TEST_GEN_PROGS := pidfd_test pidfd_open_test
> +TEST_GEN_PROGS := pidfd_test pidfd_open_test pidfd_poll_test
>
> include ../lib.mk
>
> diff --git a/tools/testing/selftests/pidfd/pidfd_poll_test.c b/tools/testing/selftests/pidfd/pidfd_poll_test.c
> new file mode 100644
> index 000000000000..f2934aa070ae
> --- /dev/null
> +++ b/tools/testing/selftests/pidfd/pidfd_poll_test.c
> @@ -0,0 +1,137 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#define _GNU_SOURCE
> +#include <errno.h>
> +#include <linux/types.h>
> +#include <linux/wait.h>
> +#include <poll.h>
> +#include <signal.h>
> +#include <stdbool.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <syscall.h>
> +#include <sys/wait.h>
> +#include <unistd.h>
> +
> +#include "pidfd.h"
> +#include "../kselftest.h"
> +
> +#define __NR_pidfd_send_signal 424
> +#define __NR_pidfd_open 434
That won't work on Alpha where this number is unfortunately different so
I'm not sure which syscall you'd hit there (/me checks
424 common tgkill sys_tgkill
)
The better option is to just place
#ifndef __NR_pidfd_send_signal
#define __NR_pidfd_send_signal -1
#endif
#ifndef __NR_pidfd_open
#define __NR_pidfd_open -1
#endif
into the pidfd.h header.
> +
> +static inline int sys_pidfd_open(pid_t pid, unsigned int flags)
> +{
> + return syscall(__NR_pidfd_open, pid, flags);
> +}
> +
> +static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
> + unsigned int flags)
> +{
> + return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
> +}
Those can go into pidfd.h too.
> +
> +static bool timeout;
> +
> +static void handle_alarm(int sig)
> +{
> + timeout = true;
> +}
> +
> +int main(int argc, char **argv)
> +{
> + int ret = 1;
> + int pidfd = -1;
> + struct pollfd fds;
> + int iter, nevents;
> + int nr_iterations = 10000;
> +
> + fds.events = POLLIN;
if (argc > 2)
ksft_exit_fail_msg("Unexpected command line argument");
> + if (argc > 1) {
if (argc == 2)
> + nr_iterations = atoi(argv[1]);
> + if (!nr_iterations) {
You should probably also check for negative values.
> + ksft_test_result_fail("invalid input parameter %s\n",
> + argv[1]);
> + return ksft_exit_fail();
> + }
> + }
> +
> + ksft_print_msg("running pidfd poll test for %d iterations\n",
> + nr_iterations);
> +
> + for (iter = 0; iter < nr_iterations; iter++) {
> + int child_pid = fork();
> +
> + if (!child_pid) {
> + /* Child process just sleeps for a min */
> + sleep(60);
> + exit(0);
Just for kicks, please use exit(EXIT_SUCCESS)
> + }
You should switch the checkes, i.e.
if (child_pid < 0)
/* do stuff */
if (child_pid == 0)
/* do other stuff */
> +
> + /* Parent kills the child and waits for its death */
> + if (child_pid < 0) {
> + if (errno == EAGAIN) {
> + iter--;
> + continue;
> + }
> + ksft_print_msg("%s - failed to fork a child process\n",
> + strerror(errno));
Uhm, shouldn't you exit with an error here?, i.e.
ksft_exit_fail_msg(...
> + }
> + pidfd = sys_pidfd_open(child_pid, 0);
> + if (pidfd < 0) {
> + ksft_print_msg("%s - pidfd_open failed\n",
> + strerror(errno));
> + goto on_error;
I think you honestly can just call ksft_exit_fail_msg() everywhere. The
fds will be cleaned up on process exit anyway and it's pretty
short-lived.
> + }
> + /* Setup 3 sec alarm - plenty of time */
> + if (signal(SIGALRM, handle_alarm) == SIG_ERR) {
> + ksft_print_msg("%s - signal failed\n",
> + strerror(errno));
> + goto on_error;
> + }
> + alarm(3);
> + /* Send SIGKILL to the child */
> + if (sys_pidfd_send_signal(pidfd, SIGKILL, NULL, 0)) {
> + ksft_print_msg("%s - pidfd_send_signal failed\n",
> + strerror(errno));
> + goto on_error;
> + }
> + /* Wait for the death notification */
> + fds.fd = pidfd;
> + nevents = poll(&fds, 1, -1);
> + if (nevents < 0) {
> + ksft_print_msg("%s - poll failed\n",
> + strerror(errno));
> + goto on_error;
> + }
> + if (nevents != 1) {
> + ksft_print_msg("unexpected poll result: %d\n",
> + nevents);
> + goto on_error;
> + }
> + if (!(fds.revents & POLLIN)) {
> + ksft_print_msg(
> + "unexpected event type received: 0x%x\n",
> + fds.revents);
> + goto on_error;
> + }
> + if (timeout) {
> + ksft_print_msg("death notification wait timeout\n");
> + goto on_error;
> + }
> + close(pidfd);
> + }
> + ret = 0;
> +
> +on_error:
> + if (pidfd)
> + close(pidfd);
> +
> + if (ret) {
> + ksft_test_result_fail("failed after %d retries\n", iter);
> + return ksft_exit_fail();
> + }
> +
> + ksft_test_result_pass("pidfd poll test: pass\n");
> + return ksft_exit_pass();
> +}
> --
> 2.22.0.657.g960e92d24f-goog
>
