tests: add pidfd poll tests

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>
Link: https://lore.kernel.org/r/20190726162226.252750-2-surenb@google.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

3 files changed, 119 insertions, 1 deletions

diff --git a/tools/testing/selftests/pidfd/.gitignore b/tools/testing/selftests/pidfd/.gitignore
index 730ef9dc08cc..8d069490e17b 100644
--- a/tools/testing/selftests/pidfd/.gitignore
+++ b/tools/testing/selftests/pidfd/.gitignore
@@ -1,3 +1,4 @@
 pidfd_open_test
+pidfd_poll_test
 pidfd_test
 pidfd_wait
diff --git a/tools/testing/selftests/pidfd/Makefile b/tools/testing/selftests/pidfd/Makefile
index 7c97e890f353..464c9b76148f 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 pidfd_wait
+TEST_GEN_PROGS := pidfd_test pidfd_open_test pidfd_poll_test pidfd_wait
 
 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..4b115444dfe9
--- /dev/null
+++ b/tools/testing/selftests/pidfd/pidfd_poll_test.c
@@ -0,0 +1,117 @@
+// 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 == 0) {
+			/* 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);
+		/* Wait for child to prevent zombies */
+		if (waitpid(child_pid, NULL, 0) < 0)
+			ksft_exit_fail_msg("%s - waitpid failed\n",
+					strerror(errno));
+
+	}
+
+	ksft_test_result_pass("pidfd poll test: pass\n");
+	return ksft_exit_pass();
+}