663f548f94
BACKGROUND The exit_group syscall, which is implicitly called by libc after the main function returns, kills all threads in a thread group, even if these threads are running, sleeping, or waiting on a futex. PROBLEM In normal use cases, exit_group does nothing since a well-written program should terminate all threads before the main function returns. But when this is not the case, exit_group can clean up the mess. Currently, Occlum does not implement exit_group. And the Occlum PAL process waits for all tasks (i.e., SGX threads) to finish before exiting. So without exit_group implemented, some tasks may be still running if after the main task exits. And this causes the Occlum PAL process to wait---forever. WORKAROUND To implement a real exit_group, we need signals to kill threads. But we do not have signals, yet. So we come up with a workaround: instead of waiting all tasks to finish in PAL, we just wait for the main task. As soon as the main task exits, the PAL process terminates, killing the remaining tasks.
84 lines
2.5 KiB
C
84 lines
2.5 KiB
C
#define _GNU_SOURCE
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#include <sys/types.h>
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#include <sys/syscall.h>
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#include <unistd.h>
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#include <pthread.h>
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#include <stdio.h>
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#include <linux/futex.h>
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#include "test.h"
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// ============================================================================
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// Test case
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// ============================================================================
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//
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// Three types of threads that will not exit voluntarily
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//
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// Type 1: a busy loop thread
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static void* busyloop_thread_func(void* _) {
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while (1) {
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// By calling getpid, we give the LibOS a chance to force the thread
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// to terminate if exit_group is called by any thread in a thread group
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getpid();
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}
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return NULL;
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}
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// Type 2: a sleeping thread
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static void* sleeping_thread_func(void* _) {
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unsigned int a_year_in_sec = 365 * 24 * 60 * 60;
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sleep(a_year_in_sec);
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return NULL;
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}
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// Type 3: a thead that keeps waiting on a futex
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static void* futex_wait_thread_func(void* _) {
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// Wait on a futex forever
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int my_private_futex = 0;
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syscall(SYS_futex, &my_private_futex, FUTEX_WAIT, my_private_futex);
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return NULL;
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}
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// exit_group syscall should terminate all threads in a thread group.
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int test_exit_group_to_force_threads_terminate(void) {
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// Create three types of threads that will not exit voluntarily
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pthread_t busyloop_thread;
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if (pthread_create(&busyloop_thread, NULL, busyloop_thread_func, NULL) < 0) {
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printf("ERROR: pthread_create failed\n");
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return -1;
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}
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pthread_t sleeping_thread;
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if (pthread_create(&sleeping_thread, NULL, sleeping_thread_func, NULL) < 0) {
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printf("ERROR: pthread_create failed\n");
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return -1;
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}
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pthread_t futex_wait_thread;
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if (pthread_create(&futex_wait_thread, NULL, futex_wait_thread_func, NULL) < 0) {
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printf("ERROR: pthread_create failed\n");
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return -1;
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}
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// Sleep for a while to make sure all three threads are running
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useconds_t _200ms = 200 * 1000;
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usleep(_200ms);
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// exit_group syscall will be called eventually by libc's exit, after the
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// main function returns. If Occlum can terminate normally, this means
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// exit_group syscall taking effect.
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return 0;
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}
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// ============================================================================
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// Test suite
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// ============================================================================
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static test_case_t test_cases[] = {
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TEST_CASE(test_exit_group_to_force_threads_terminate)
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};
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int main() {
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return test_suite_run(test_cases, ARRAY_SIZE(test_cases));
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}
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