Merge pull request #553 from rodionov/new_tgid

Enable creation of host tasks with new tgid in LKL.

arch/lkl/include/asm/unistd.h

@@ -1,6 +1,7 @@
 #include <uapi/asm/unistd.h>
 
 __SYSCALL(__NR_virtio_mmio_device_add, sys_virtio_mmio_device_add)
+__SYSCALL(__NR_new_thread_group_leader, sys_new_thread_group_leader)
 
 #define __SC_ASCII(t, a) #t "," #a
 

arch/lkl/include/uapi/asm/unistd.h

@@ -15,3 +15,4 @@
 #include <asm-generic/unistd.h>
 
 #define __NR_virtio_mmio_device_add		(__NR_arch_specific_syscall + 0)
+#define __NR_new_thread_group_leader	(__NR_arch_specific_syscall + 1)

arch/lkl/kernel/syscalls.c

@@ -19,6 +19,8 @@
 static asmlinkage long sys_virtio_mmio_device_add(long base, long size,
 						  unsigned int irq);
 
+static asmlinkage long sys_new_thread_group_leader(void);
+
 typedef long (*syscall_handler_t)(long arg1, ...);
 
 #undef __SYSCALL
@@ -55,13 +57,17 @@ static long run_syscall(long no, long *params)
 static int host_task_id;
 static struct task_struct *host0;
 
-static int new_host_task(struct task_struct **task)
+static int new_host_task(struct task_struct **task, int new_tg_leader)
 {
 	pid_t pid;
+	unsigned long flags = CLONE_FLAGS;
 
 	switch_to_host_task(host0);
 
-	pid = kernel_thread(host_task_stub, NULL, NULL, CLONE_FLAGS);
+	if (new_tg_leader)
+		flags &= ~CLONE_THREAD;
+
+	pid = kernel_thread(host_task_stub, NULL, NULL, flags);
 	if (pid < 0)
 		return pid;
 
@@ -108,7 +114,7 @@ long lkl_syscall(long no, long *params)
 	if (lkl_ops->tls_get) {
 		task = lkl_ops->tls_get(task_key);
 		if (!task) {
-			ret = new_host_task(&task);
+			ret = new_host_task(&task, no == __NR_new_thread_group_leader);
 			if (ret)
 				goto out;
 			lkl_ops->tls_set(task_key, task);
@@ -164,6 +170,15 @@ int syscalls_init(void)
 	set_thread_flag(TIF_HOST_THREAD);
 	host0 = current;
 
+	// Reap zombie host tasks spawned as new thread group leaders via
+	// new_thread_group_leader syscall (otherwise the dead task resources
+	// such as `struct task_struct` won't be reclaimed by kernel).
+	// TODO: currently LKL doesn't support thread signal handling in
+	// user-space, thus, it's safe to ignore this signal here. However,
+	// if user-space signal handling is implemented in future we might want
+	// to remove the line of code below to let user-space handle SIGCHLD.
+	kernel_sigaction(SIGCHLD, SIG_IGN);
+
 	if (lkl_ops->tls_alloc) {
 		task_key = lkl_ops->tls_alloc(del_host_task);
 		if (!task_key)
@@ -239,3 +254,13 @@ SYSCALL_DEFINE3(virtio_mmio_device_add, long, base, long, size, unsigned int,
 
 	return ret;
 }
+
+
+SYSCALL_DEFINE0(new_thread_group_leader)
+{
+	// No-op here -- actual handling is done in lkl_syscall routine.
+	if (current->tgid == current->pid)
+		return 0;
+	else
+		return -1;
+}

tools/lkl/tests/boot.c

@@ -479,6 +479,73 @@ static int lkl_test_many_syscall_threads(void)
 
 	return TEST_SUCCESS;
 }
+
+struct lkl_test_tgid {
+	long tgid;
+	long parent_pid;
+	int new_thread_group_leader_result;
+};
+
+static void thread_get_tgid(void *arg)
+{
+	struct lkl_test_tgid *tgid_arg = (struct lkl_test_tgid *)arg;
+
+	int ret = lkl_sys_new_thread_group_leader();
+
+	tgid_arg->new_thread_group_leader_result = ret;
+	if (!ret) {
+		tgid_arg->tgid = lkl_sys_getpid();
+		tgid_arg->parent_pid = lkl_sys_getppid();
+	}
+}
+
+static int lkl_test_new_tgid_threads(void)
+{
+	lkl_thread_t tid;
+	long current_pid;
+	int count = 65, ret;
+	struct lkl_test_tgid test_tgid;
+
+	current_pid = lkl_sys_getpid();
+	if (current_pid < 0) {
+		lkl_test_logf("failed to get pid\n");
+		return TEST_FAILURE;
+	}
+
+	while (--count > 0) {
+		tid = lkl_host_ops.thread_create(thread_get_tgid, &test_tgid);
+		if (!tid) {
+			lkl_test_logf("failed to create thread\n");
+			return TEST_FAILURE;
+		}
+
+		ret = lkl_host_ops.thread_join(tid);
+		if (ret) {
+			lkl_test_logf("failed to join thread\n");
+			return TEST_FAILURE;
+		}
+
+		if (test_tgid.new_thread_group_leader_result) {
+			lkl_test_logf("failed to set new thread group leader %x\n",
+				test_tgid.new_thread_group_leader_result);
+			return TEST_FAILURE;
+		}
+
+		if (test_tgid.tgid == current_pid) {
+			lkl_test_logf("child tgid %lx == current pid %lx\n",
+				test_tgid.tgid, current_pid);
+			return TEST_FAILURE;
+		}
+
+		if (test_tgid.parent_pid != current_pid) {
+			lkl_test_logf("ppid of the child %lx != current pid %lx\n",
+				test_tgid.parent_pid, current_pid);
+			return TEST_FAILURE;
+		}
+	}
+
+	return TEST_SUCCESS;
+}
 #endif
 
 static void thread_quit_immediately(void *unused)
@@ -694,6 +761,7 @@ struct lkl_test tests[] = {
 	 */
 #ifndef __MINGW32__
 	LKL_TEST(many_syscall_threads),
+	LKL_TEST(new_tgid_threads),
 #endif
 #ifdef LKL_HOST_CONFIG_MMU
 	LKL_TEST(shared_mmap),