restore: Block SIGCHLD during root_item initialization

(Was "user_ns: Block SIGCHLD during namespaces generation")

We don't want asynchronous signal handler during creation
of namespaces (for example, in create_user_ns_hierarhy())
as we do wait() synchronous. So we need to block the signal.
Do this once globally.

v2: Set initial ret = 0
v3: Block signal globally in root_item before its children
are created.
v4: Move block to prepare_namespace()
Suggested-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/include/util.h

@@ -346,4 +346,25 @@ extern int epoll_prepare(int nr_events, struct epoll_event **evs);
 
 extern int call_in_child_process(int (*fn)(void *), void *arg);
 
+#define block_sigmask(saved_mask, sig_mask)	({					\
+		sigset_t ___blocked_mask;						\
+		int ___ret = 0;								\
+		sigemptyset(&___blocked_mask);						\
+		sigaddset(&___blocked_mask, sig_mask);					\
+		if (sigprocmask(SIG_BLOCK, &___blocked_mask, saved_mask) == -1) {	\
+			pr_perror("Can not set mask of blocked signals");		\
+			___ret = -1;							\
+		}									\
+		___ret;									\
+	})
+
+#define restore_sigmask(saved_mask)	({						\
+		int ___ret = 0;								\
+		if (sigprocmask(SIG_SETMASK, saved_mask, NULL) == -1) {			\
+			pr_perror("Can not unset mask of blocked signals");		\
+			___ret = -1;							\
+		}									\
+		___ret;									\
+	})
+
 #endif /* __CR_UTIL_H__ */

criu/namespaces.c

@@ -1682,11 +1682,15 @@ err_out:
 int prepare_namespace(struct pstree_item *item, unsigned long clone_flags)
 {
 	pid_t pid = vpid(item);
-	int id;
+	sigset_t sig_mask;
+	int id, ret = -1;
 
 	pr_info("Restoring namespaces %d flags 0x%lx\n",
 			vpid(item), clone_flags);
 
+	if (block_sigmask(&sig_mask, SIGCHLD) < 0)
+		return -1;
+
 	if ((clone_flags & CLONE_NEWUSER) && prepare_userns_creds())
 		return -1;
 
@@ -1698,22 +1702,27 @@ int prepare_namespace(struct pstree_item *item, unsigned long clone_flags)
 
 	id = ns_per_id ? item->ids->uts_ns_id : pid;
 	if ((clone_flags & CLONE_NEWUTS) && prepare_utsns(id))
-		return -1;
+		goto out;
 	id = ns_per_id ? item->ids->ipc_ns_id : pid;
 	if ((clone_flags & CLONE_NEWIPC) && prepare_ipc_ns(id))
-		return -1;
+		goto out;
 
 	if (prepare_net_namespaces())
-		return -1;
+		goto out;
 
 	/*
 	 * This one is special -- there can be several mount
 	 * namespaces and prepare_mnt_ns handles them itself.
 	 */
 	if (prepare_mnt_ns())
-		return -1;
+		goto out;
 
-	return 0;
+	ret = 0;
+out:
+	if (restore_sigmask(&sig_mask) < 0)
+		ret = -1;
+
+	return ret;
 }
 
 int prepare_namespace_before_tasks(void)