1 files changed, 323 insertions, 0 deletions
diff --git a/test/kworker-hang.c b/test/kworker-hang.c
new file mode 100644
index 0000000..15147c6
--- /dev/null
+++ b/test/kworker-hang.c
@@ -0,0 +1,323 @@
+/* SPDX-License-Identifier: MIT */
+
+/*
+ * kworker-hang
+ *
+ * Link: https://github.com/axboe/liburing/issues/448
+ */
+
+#include <dirent.h>
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/poll.h>
+#include <sys/eventfd.h>
+#include <sys/resource.h>
+#include <sys/wait.h>
+
+#include "helpers.h"
+#include "liburing.h"
+
+#define NR_RINGS			2
+
+/*
+ * WAIT_FOR_KWORKER_SECS can be any longer, but to make
+ * the test short, 10 seconds should be enough.
+ */
+#define WAIT_FOR_KWORKER_SECS		10
+#define WAIT_FOR_KWORKER_SECS_STR	"10"
+
+static bool is_all_numeric(const char *pid)
+{
+	size_t i, l;
+	char c;
+
+	l = strnlen(pid, 32);
+	if (l == 0)
+		return false;
+
+	for (i = 0; i < l; i++) {
+		c = pid[i];
+		if (!('0' <= c && c <= '9'))
+			return false;
+	}
+
+	return true;
+}
+
+static bool is_kworker_event_unbound(const char *pid)
+{
+	int fd;
+	bool ret = false;
+	char fpath[256];
+	char read_buf[256] = { };
+	ssize_t read_size;
+
+	snprintf(fpath, sizeof(fpath), "/proc/%s/comm", pid);
+
+	fd = open(fpath, O_RDONLY);
+	if (fd < 0)
+		return false;
+
+	read_size = read(fd, read_buf, sizeof(read_buf) - 1);
+	if (read_size < 0)
+		goto out;
+
+	if (!strncmp(read_buf, "kworker", 7) && strstr(read_buf, "events_unbound"))
+		ret = true;
+out:
+	close(fd);
+	return ret;
+}
+
+static bool is_on_io_ring_exit_work(const char *pid)
+{
+	int fd;
+	bool ret = false;
+	char fpath[256];
+	char read_buf[4096] = { };
+	ssize_t read_size;
+
+	snprintf(fpath, sizeof(fpath), "/proc/%s/stack", pid);
+
+	fd = open(fpath, O_RDONLY);
+	if (fd < 0)
+		return false;
+
+	read_size = read(fd, read_buf, sizeof(read_buf) - 1);
+	if (read_size < 0)
+		goto out;
+
+	if (strstr(read_buf, "io_ring_exit_work"))
+		ret = true;
+out:
+	close(fd);
+	return ret;
+}
+
+static bool is_in_d_state(const char *pid)
+{
+	int fd;
+	bool ret = false;
+	char fpath[256];
+	char read_buf[4096] = { };
+	ssize_t read_size;
+	const char *p = read_buf;
+
+	snprintf(fpath, sizeof(fpath), "/proc/%s/stat", pid);
+
+	fd = open(fpath, O_RDONLY);
+	if (fd < 0)
+		return false;
+
+	read_size = read(fd, read_buf, sizeof(read_buf) - 1);
+	if (read_size < 0)
+		goto out;
+
+	/*
+	 * It looks like this:
+	 * 9384 (kworker/u8:8+events_unbound) D 2 0 0 0 -1 69238880 0 0 0 0 0 0 0 0 20 0 1 0
+	 *
+	 * Catch the 'D'!
+	 */
+	while (*p != ')') {
+		p++;
+		if (&p[2] >= &read_buf[sizeof(read_buf) - 1])
+			/*
+			 * /proc/$pid/stack shows the wrong output?
+			 */
+			goto out;
+	}
+
+	ret = (p[2] == 'D');
+out:
+	close(fd);
+	return ret;
+}
+
+/*
+ * Return 1 if we have kworkers hang or fail to open `/proc`.
+ */
+static int scan_kworker_hang(void)
+{
+	DIR *dr;
+	int ret = 0;
+	struct dirent *de;
+
+	dr = opendir("/proc");
+	if (dr == NULL) {
+		perror("opendir");
+		return 1;
+	}
+
+	while (1) {
+		const char *pid;
+
+		de = readdir(dr);
+		if (!de)
+			break;
+
+		pid = de->d_name;
+		if (!is_all_numeric(pid))
+			continue;
+
+		if (!is_kworker_event_unbound(pid))
+			continue;
+
+		if (!is_on_io_ring_exit_work(pid))
+			continue;
+
+		if (is_in_d_state(pid)) {
+			/* kworker hang */
+			fprintf(stderr, "Bug: found hang kworker on "
+				"io_ring_exit_work /proc/%s\n", pid);
+			ret = 1;
+		}
+	}
+
+	closedir(dr);
+	return ret;
+}
+
+static void set_hung_entries(void)
+{
+	const char *cmds[] = {
+		/* Backup current values. */
+		"cat /proc/sys/kernel/hung_task_all_cpu_backtrace > hung_task_all_cpu_backtrace.bak",
+		"cat /proc/sys/kernel/hung_task_check_count > hung_task_check_count.bak",
+		"cat /proc/sys/kernel/hung_task_panic > hung_task_panic.bak",
+		"cat /proc/sys/kernel/hung_task_check_interval_secs > hung_task_check_interval_secs.bak",
+		"cat /proc/sys/kernel/hung_task_timeout_secs > hung_task_timeout_secs.bak",
+		"cat /proc/sys/kernel/hung_task_warnings > hung_task_warnings.bak",
+
+		/* Set to do the test. */
+		"echo 1 > /proc/sys/kernel/hung_task_all_cpu_backtrace",
+		"echo 99999999 > /proc/sys/kernel/hung_task_check_count",
+		"echo 0 > /proc/sys/kernel/hung_task_panic",
+		"echo 1 > /proc/sys/kernel/hung_task_check_interval_secs",
+		"echo " WAIT_FOR_KWORKER_SECS_STR " > /proc/sys/kernel/hung_task_timeout_secs",
+		"echo -1 > /proc/sys/kernel/hung_task_warnings",
+	};
+	int p;
+	size_t i;
+
+	for (i = 0; i < ARRAY_SIZE(cmds); i++)
+		p = system(cmds[i]);
+
+	(void)p;
+}
+
+static void restore_hung_entries(void)
+{
+	const char *cmds[] = {
+		/* Restore old values. */
+		"cat hung_task_all_cpu_backtrace.bak > /proc/sys/kernel/hung_task_all_cpu_backtrace",
+		"cat hung_task_check_count.bak > /proc/sys/kernel/hung_task_check_count",
+		"cat hung_task_panic.bak > /proc/sys/kernel/hung_task_panic",
+		"cat hung_task_check_interval_secs.bak > /proc/sys/kernel/hung_task_check_interval_secs",
+		"cat hung_task_timeout_secs.bak > /proc/sys/kernel/hung_task_timeout_secs",
+		"cat hung_task_warnings.bak > /proc/sys/kernel/hung_task_warnings",
+
+		/* Clean up! */
+		"rm -f " \
+			"hung_task_all_cpu_backtrace.bak " \
+			"hung_task_check_count.bak " \
+			"hung_task_panic.bak " \
+			"hung_task_check_interval_secs.bak " \
+			"hung_task_timeout_secs.bak " \
+			"hung_task_warnings.bak"
+	};
+	int p;
+	size_t i;
+
+	for (i = 0; i < ARRAY_SIZE(cmds); i++)
+		p = system(cmds[i]);
+
+	(void)p;
+}
+
+
+static int run_child(void)
+{
+	int ret, i;
+	struct io_uring rings[NR_RINGS];
+
+	for (i = 0; i < NR_RINGS; i++) {
+		struct io_uring_params p = { };
+
+		ret = io_uring_queue_init_params(64, &rings[i], &p);
+		if (ret) {
+			fprintf(stderr, "io_uring_queue_init_params(): (%d) %s\n",
+			        ret, strerror(-ret));
+			return 1;
+		}
+	}
+
+	for (i = 0; i < NR_RINGS; i++)
+		io_uring_queue_exit(&rings[i]);
+
+	kill(getpid(), SIGSTOP);
+	/*
+	 * kworkers hang right after this task sends SIGSTOP to itself.
+	 * The parent process will check it. We are suspended here!
+	 */
+	return 0;
+}
+
+int main(void)
+{
+	pid_t child_pid;
+	int ret, wstatus = 0;
+
+	/*
+	 * We need root to check /proc/$pid/stack and set /proc/sys/kernel/hung*
+	 */
+	if (getuid() != 0 && geteuid() != 0) {
+		fprintf(stderr, "Skipping kworker-hang: not root\n");
+		return 0;
+	}
+
+	set_hung_entries();
+	child_pid = fork();
+	if (child_pid < 0) {
+		ret = errno;
+		fprintf(stderr, "fork(): (%d) %s\n", ret, strerror(ret));
+		restore_hung_entries();
+		return 1;
+	}
+
+	if (!child_pid)
+		return run_child();
+
+	atexit(restore_hung_entries);
+
+	/*
+	 * +2 just to add small extra time for
+	 * fork(), io_uring_setup(), close(), etc.
+	 */
+	sleep(WAIT_FOR_KWORKER_SECS + 2);
+	ret = scan_kworker_hang();
+
+	/*
+	 * Continue the suspended task.
+	 */
+	kill(child_pid, SIGCONT);
+
+	if (waitpid(child_pid, &wstatus, 0) < 0) {
+		ret = errno;
+		fprintf(stderr, "waitpid(): (%d) %s\n", ret, strerror(ret));
+		return 1;
+	}
+
+	if (!WIFEXITED(wstatus)) {
+		fprintf(stderr, "Child process won't exit\n");
+		return 1;
+	}
+
+	/* Make sure child process exited properly as well. */
+	return ret | WEXITSTATUS(wstatus);
+}