Re: [PATCH v2 2/2] tests: add pidfd poll tests

[Yann Droneaud <ydroneaud@opteya.com>]

Hi,

Le mercredi 24 juillet 2019 à 17:22 -0700, Suren Baghdasaryan a écrit :
> 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")
> 
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
>  tools/testing/selftests/pidfd/.gitignore      |   1 +
>  tools/testing/selftests/pidfd/Makefile        |   2 +-
>  .../testing/selftests/pidfd/pidfd_poll_test.c | 112 ++++++++++++++++++
>  3 files changed, 114 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..d45c612a0fe5
> --- /dev/null
> +++ b/tools/testing/selftests/pidfd/pidfd_poll_test.c
> @@ -0,0 +1,112 @@
> +// 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"
> +
> +static bool timeout;
> +
> +static void handle_alarm(int sig)
> +{
> +	timeout = true;
> +}
> +
> +int main(int argc, char **argv)
> +{
> +	struct pollfd fds;
> +	int iter, nevents;
> +	int nr_iterations = 10000;
> +
> +	fds.events = POLLIN;
> +
> +	if (argc > 2)
> +		ksft_exit_fail_msg("Unexpected command line argument\n");
> +
> +	if (argc == 2) {
> +		nr_iterations = atoi(argv[1]);
> +		if (nr_iterations <= 0)
> +			ksft_exit_fail_msg("invalid input parameter %s\n",
> +					argv[1]);
> +	}
> +
> +	ksft_print_msg("running pidfd poll test for %d iterations\n",
> +		nr_iterations);
> +
> +	for (iter = 0; iter < nr_iterations; iter++) {
> +		int pidfd;
> +		int child_pid = fork();
> +
> +		if (child_pid < 0) {
> +			if (errno == EAGAIN) {
> +				iter--;
> +				continue;
> +			}
> +			ksft_exit_fail_msg(
> +				"%s - failed to fork a child process\n",
> +				strerror(errno));
> +		}
> +
> +		if (!child_pid) {
> +			/* Child process just sleeps for a min and exits */
> +			sleep(60);
> +			exit(EXIT_SUCCESS);
> +		}
> +
> +		/* Parent kills the child and waits for its death */
> +		pidfd = sys_pidfd_open(child_pid, 0);
> +		if (pidfd < 0)
> +			ksft_exit_fail_msg("%s - pidfd_open failed\n",
> +					strerror(errno));
> +
> +		/* Setup 3 sec alarm - plenty of time */
> +		if (signal(SIGALRM, handle_alarm) == SIG_ERR)
> +			ksft_exit_fail_msg("%s - signal failed\n",
> +					strerror(errno));
> +		alarm(3);
> +
> +		/* Send SIGKILL to the child */
> +		if (sys_pidfd_send_signal(pidfd, SIGKILL, NULL, 0))
> +			ksft_exit_fail_msg("%s - pidfd_send_signal failed\n",
> +					strerror(errno));
> +
> +		/* Wait for the death notification */
> +		fds.fd = pidfd;
> +		nevents = poll(&fds, 1, -1);
> +
> +		/* Check for error conditions */
> +		if (nevents < 0)
> +			ksft_exit_fail_msg("%s - poll failed\n",
> +					strerror(errno));
> +
> +		if (nevents != 1)
> +			ksft_exit_fail_msg("unexpected poll result: %d\n",
> +					nevents);
> +
> +		if (!(fds.revents & POLLIN))
> +			ksft_exit_fail_msg(
> +				"unexpected event type received: 0x%x\n",
> +				fds.revents);
> +
> +		if (timeout)
> +			ksft_exit_fail_msg(
> +				"death notification wait timeout\n");
> +
> +		close(pidfd);

There's no call to wait(), or alike function. Is it required for the
test to left zombies ?

Regards.

-- 
Yann Droneaud
OPTEYA