[CRIU] [PATCH v3] restore: Block SIGCHLD during root_item initialization

[Kirill Tkhai]

(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 (till creation of real children of
root_item).

v2: Set initial ret = 0
v3: Block signal globally in root_item before its children
are created.

https://travis-ci.org/tkhai/criu

Suggested-by: Andrew Vagin <avagin at virtuozzo.com>
Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 criu/cr-restore.c   |   11 +++++++++++
 criu/include/util.h |   21 +++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/criu/cr-restore.c b/criu/cr-restore.c
index 7842e169e..2ae2fd172 100644
--- a/criu/cr-restore.c
+++ b/criu/cr-restore.c
@@ -1326,6 +1326,8 @@ static int create_children_and_session(void)
 static int restore_task_with_children(void *_arg)
 {
 	struct cr_clone_arg *ca = _arg;
+	bool sig_blocked = false;
+	sigset_t sig_mask;
 	pid_t pid;
 	int ret;
 
@@ -1337,6 +1339,10 @@ static int restore_task_with_children(void *_arg)
 				current->pid->real, vpid(current));
 		if (current->pid->real < 0)
 			goto err;
+	} else {
+		if (block_sigmask(&sig_mask, SIGCHLD) < 0)
+			goto err;
+		sig_blocked = true;
 	}
 
 	if ( !(ca->clone_flags & CLONE_FILES))
@@ -1438,6 +1444,9 @@ static int restore_task_with_children(void *_arg)
 		BUG();
 	}
 
+	if (sig_blocked && restore_sigmask(&sig_mask) < 0)
+		goto err;
+
 	if (create_children_and_session())
 		goto err;
 
@@ -1469,6 +1478,8 @@ static int restore_task_with_children(void *_arg)
 	return 0;
 
 err:
+	if (sig_blocked)
+		restore_sigmask(&sig_mask);
 	if (current->parent == NULL)
 		futex_abort_and_wake(&task_entries->nr_in_progress);
 	exit(1);
diff --git a/criu/include/util.h b/criu/include/util.h
index 0428490bd..91587ef1c 100644
--- a/criu/include/util.h
+++ b/criu/include/util.h
@@ -311,4 +311,25 @@ extern int open_fd_of_real_pid(pid_t pid, int fd, int flags);
 
 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__ */