On Thu, Jul 25, 2019 at 1:57 PM Yann Droneaud ydroneaud@opteya.com wrote:
Hi,
Le jeudi 25 juillet 2019 à 08:48 -0700, Suren Baghdasaryan a écrit :
On Thu, Jul 25, 2019 at 4:58 AM Yann Droneaud ydroneaud@opteya.com wrote:
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 ?
The test checks that death notification gets sent from kernel, which by design should happen for any process that has non-zero task->exit_state and that includes zombies (see https://elixir.bootlin.com/linux/v5.3-rc1/source/kernel/fork.c#L1731 for that condition). So IIUC this code, the poll() should succeed no matter if the task is zombie or dead. Or do I misunderstand your question?
OK, so I think it would be better to call wait() (in the future pidfd_wait()) to reap processes as they die.
I'm not afraid by one zombie, but herding an army of 10000 zombie processes is another matter :)
Ah, I see what you mean now. I can respin this patch with a wait(child_pid, NULL, 0) after close(pidfd) call. Would that address your concern?
Regards.
-- Yann Droneaud OPTEYA
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