cgroup: make memory.kmem.limit_in_bytes a "special" property

This property can't be written after there are children of the current
cgroup or once it has tasks, similar to the cpuset properties. So, let's
hoist this property into the "special" array.
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/cgroup.c

@@ -927,9 +927,13 @@ static int ctrl_dir_and_opt(CgControllerEntry *ctl, char *dir, int ds,
 	return doff;
 }
 
-static const char *special_cpuset_props[] = {
+/* Some properties cannot be restored after the cgroup has children or tasks in
+ * it. We restore these properties as soon as the cgroup is created.
+ */
+static const char *special_props[] = {
 	"cpuset.cpus",
 	"cpuset.mems",
+	"memory.kmem.limit_in_bytes",
 	NULL,
 };
 
@@ -1270,8 +1274,8 @@ static int prepare_cgroup_dir_properties(char *path, int off, CgroupDirEntry **e
 				 * the restore to fail if some other task has
 				 * entered the cgroup.
 				 */
-				for (k = 0; special_cpuset_props[k]; k++) {
-					if (!strcmp(e->properties[j]->name, special_cpuset_props[k])) {
+				for (k = 0; special_props[k]; k++) {
+					if (!strcmp(e->properties[j]->name, special_props[k])) {
 						special = true;
 						break;
 					}
@@ -1353,14 +1357,14 @@ int prepare_cgroup_properties(void)
 	return 0;
 }
 
-static int restore_special_cpuset_props(char *paux, size_t off, CgroupDirEntry *e)
+static int restore_special_props(char *paux, size_t off, CgroupDirEntry *e)
 {
 	int i, j;
 
-	pr_info("Restore special cpuset props\n");
+	pr_info("Restore special props\n");
 
-	for (i = 0; special_cpuset_props[i]; i++) {
-		const char *name = special_cpuset_props[i];
+	for (i = 0; special_props[i]; i++) {
+		const char *name = special_props[i];
 
 		for (j = 0; j < e->n_properties; j++) {
 			CgroupPropEntry *prop = e->properties[j];
@@ -1423,8 +1427,8 @@ static int prepare_cgroup_dirs(char **controllers, int n_controllers, char *paux
 				return -1;
 
 			for (j = 0; j < n_controllers; j++) {
-				if (strcmp(controllers[j], "cpuset") == 0) {
-					if (restore_special_cpuset_props(paux, off2, e) < 0) {
+				if (!strcmp(controllers[j], "cpuset") || !strcmp(controllers[j], "memory")) {
+					if (restore_special_props(paux, off2, e) < 0) {
 						pr_err("Restoring special cpuset props failed!\n");
 						return -1;
 					}