restore: collect signals from zombies (v4)

Each zombie sends SIGCHLD to parent. crtools restores all pending
signals, so all other signals should be collected.

Here is a problems, that signals SIGCHLD can be merged, but crtools
should be sure, that all signals are collected.

For that a zombie locks a global zombie_lock, which is released by
parent.

This operation should be done between CR_STATE_RESTORE and
CR_STATE_RESTORE_SIGCHLD.

Here is one more CR_STATE_RESTORE_ZOMBIES, whic is used for waiting all
zombies.

v2: clean up
v3: rework synchronization
v4: rework without additional CR_STATE-s
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-restore.c

@@ -719,7 +719,7 @@ static int restore_one_zombie(int pid, int exit_code)
 	if (task_entries != NULL) {
 		restore_finish_stage(CR_STATE_RESTORE);
 		zombie_prepare_signals();
-		restore_finish_stage(CR_STATE_RESTORE_SIGCHLD);
+		mutex_lock(&task_entries->zombie_lock);
 	}
 
 	if (exit_code & 0x7f) {
@@ -1286,6 +1286,7 @@ static int prepare_task_entries()
 	task_entries->nr_tasks = 0;
 	task_entries->nr_helpers = 0;
 	futex_set(&task_entries->start, CR_STATE_FORKING);
+	mutex_init(&task_entries->zombie_lock);
 
 	return 0;
 }
@@ -2049,6 +2050,7 @@ static int sigreturn_restore(pid_t pid, CoreEntry *core)
 	 * Now prepare run-time data for threads restore.
 	 */
 	task_args->nr_threads		= current->nr_threads;
+	task_args->nr_zombies		= current->rst->nr_zombies;
 	task_args->clone_restore_fn	= (void *)restore_thread_exec_start;
 	task_args->thread_args		= thread_args;
 

include/restorer.h

@@ -98,6 +98,7 @@ struct task_restore_core_args {
 
 	/* threads restoration */
 	int				nr_threads;		/* number of threads */
+	int				nr_zombies;
 	thread_restore_fcall_t		clone_restore_fn;	/* helper address for clone() call */
 	struct thread_restore_args	*thread_args;		/* array of thread arguments */
 	struct shmems			*shmems;
@@ -170,6 +171,7 @@ struct task_entries {
 	int nr_threads, nr_tasks, nr_helpers;
 	futex_t nr_in_progress;
 	futex_t start;
+	mutex_t	zombie_lock;
 };
 
 static always_inline struct shmem_info *

pie/restorer.c

@@ -39,6 +39,7 @@
 
 static struct task_entries *task_entries;
 static futex_t thread_inprogress;
+static futex_t zombies_inprogress;
 
 extern void cr_restore_rt (void) asm ("__cr_restore_rt")
 			__attribute__ ((visibility ("hidden")));
@@ -47,6 +48,15 @@ static void sigchld_handler(int signal, siginfo_t *siginfo, void *data)
 {
 	char *r;
 
+	if (futex_get(&task_entries->start) == CR_STATE_RESTORE_SIGCHLD) {
+		pr_debug("%ld: Collect a zombie with (pid %d, %d)\n",
+			sys_getpid(), siginfo->si_pid, siginfo->si_pid);
+		futex_dec_and_wake(&task_entries->nr_in_progress);
+		futex_dec_and_wake(&zombies_inprogress);
+		mutex_unlock(&task_entries->zombie_lock);
+		return;
+	}
+
 	if (siginfo->si_code & CLD_EXITED)
 		r = " exited, status=";
 	else if (siginfo->si_code & CLD_KILLED)
@@ -732,8 +742,12 @@ long __export_restore_task(struct task_restore_core_args *args)
 
 	pr_info("%ld: Restored\n", sys_getpid());
 
+	futex_set(&zombies_inprogress, args->nr_zombies);
+
 	restore_finish_stage(CR_STATE_RESTORE);
 
+	futex_wait_while_gt(&zombies_inprogress, 0);
+
 	sys_sigaction(SIGCHLD, &args->sigchld_act, NULL, sizeof(k_rtsigset_t));
 
 	ret = restore_signals(args->siginfo, args->siginfo_nr, true);