[CRIU] [PATCH RFC] namespaces: use CLONE_VFORK with CLONE_VM when it is possible

[Andrei Vagin]

From: Andrei Vagin <avagin at virtuozzo.com>

We use CLONE_VM to dump and restore namespaces. Currently we allocate
a new stack, but CLONE_VFORK allows to work on the current stack, because
a parent process is frozen while a child process is running.

Signed-off-by: Andrei Vagin <avagin at virtuozzo.com>
---
 criu/clone-noasan.c |  8 ++++----
 criu/namespaces.c   | 18 +++++-------------
 2 files changed, 9 insertions(+), 17 deletions(-)

diff --git a/criu/clone-noasan.c b/criu/clone-noasan.c
index c5171b1..1b19f3e 100644
--- a/criu/clone-noasan.c
+++ b/criu/clone-noasan.c
@@ -19,13 +19,13 @@
  */
 int clone_noasan(int (*fn)(void *), int flags, void *arg)
 {
+	int ret;
 	/*
 	 * Reserve some space for clone() to locate arguments
-	 * and retcode in this place
+	 * and retcode in this place. stack_ptr is set out of the current used
+	 * stack to be able to use CLONE_VFORK | CLONE_VM.
 	 */
-	char stack[128] __stack_aligned__;
-	char *stack_ptr = &stack[sizeof(stack)];
-	int ret;
+	void *stack_ptr = (void *) round_down(((unsigned long) &ret) - 256, 16);
 
 	ret = clone(fn, stack_ptr, flags, arg);
 	return ret;
diff --git a/criu/namespaces.c b/criu/namespaces.c
index a4c3063..f3bcbbd 100644
--- a/criu/namespaces.c
+++ b/criu/namespaces.c
@@ -33,6 +33,7 @@
 #include "common/scm.h"
 #include "fdstore.h"
 #include "proc_parse.h"
+#include "clone-noasan.h"
 
 static struct ns_desc *ns_desc_array[] = {
 	&net_ns_desc,
@@ -985,19 +986,17 @@ static int dump_user_ns(void *arg)
 
 	if (switch_ns(ns->parent->ns_pid, &user_ns_desc, NULL) < 0) {
 		pr_err("Can't enter user namespace\n");
-		return -1;
+		_exit(1);
 	}
-
-	return __dump_user_ns(ns);
+	_exit(__dump_user_ns(ns) == 0 ? 0 : 1);
 }
 
 int collect_user_ns(struct ns_id *ns, void *oarg)
 {
-	int status, stack_size;
+	int status;
 	struct ns_id *p_ns;
 	pid_t pid = -1;
 	UsernsEntry *e;
-	char *stack;
 
 	p_ns = ns->parent;
 
@@ -1026,13 +1025,7 @@ int collect_user_ns(struct ns_id *ns, void *oarg)
 		 * may do changes about CRIU's internal files states in memory,
 		 * so pass CLONE_FILES to reflect that.
 		 */
-		stack_size = 2 * 1024 * 1024;
-		stack = mmap(NULL, stack_size, PROT_WRITE | PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
-		if (stack == MAP_FAILED) {
-			pr_perror("Can't allocate stack");
-			return -1;
-		}
-		pid = clone(dump_user_ns, stack + stack_size, CLONE_VM | CLONE_FILES | SIGCHLD, ns);
+		pid = clone_noasan(dump_user_ns, CLONE_VM | CLONE_FILES | SIGCHLD | CLONE_VFORK, ns);
 		if (pid == -1) {
 			pr_perror("Can't clone");
 			return -1;
@@ -1045,7 +1038,6 @@ int collect_user_ns(struct ns_id *ns, void *oarg)
 			pr_err("Can't dump nested user_ns: %x\n", status);
 			return -1;
 		}
-		munmap(stack, stack_size);
 		return 0;
 	} else {
 		if (__dump_user_ns(ns))
-- 
2.7.4