mount: Build mount tree on dump restore early, if needed

For paths resolution we will need mount tree to be parsed
and built, but it's not that simple -- the current code
implies that once parsed the tree must not be re-parsed
again, so we pass @parse argument from a caller: if a task
we're restoring do not use mount namespace, we should parse
mount tree early, otherwise defer this action until mount
tree is read from the image.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-dump.c

@@ -1703,7 +1703,7 @@ int cr_dump_tasks(pid_t pid)
 	if (collect_file_locks())
 		goto err;
 
-	if (collect_mount_info(pid))
+	if (collect_mount_info(pid, true))
 		goto err;
 
 	if (mntns_collect_root(root_item->pid.real))

cr-restore.c

@@ -1260,7 +1260,14 @@ static int restore_task_with_children(void *_arg)
 
 	/* Restore root task */
 	if (current->parent == NULL) {
-		if (collect_mount_info(getpid()))
+		/*
+		 * For ghost file path resolving on BTRFS we will need
+		 * parsed mount tree, but IIF we're not restoring task
+		 * with mount namespace cloned, in this case we don't parse
+		 * mount tree early because we will be reading mount points
+		 * from image later and generate new mount tree.
+		 */
+		if (collect_mount_info(getpid(), !(ca->clone_flags & CLONE_NEWNS)))
 			exit(1);
 
 		if (prepare_namespace(current, ca->clone_flags))

include/mount.h

@@ -7,7 +7,7 @@ extern int mntns_collect_root(pid_t pid);
 struct proc_mountinfo;
 
 extern int open_mount(unsigned int s_dev);
-extern int collect_mount_info(pid_t pid);
+extern int collect_mount_info(pid_t pid, bool parse);
 extern struct fstype *find_fstype_by_name(char *fst);
 
 struct cr_fdset;

mount.c

@@ -33,6 +33,9 @@ int mntns_root = -1;
 static DIR *open_mountpoint(struct mount_info *pm);
 static int close_mountpoint(DIR *dfd);
 
+static struct mount_info *mnt_build_tree(struct mount_info *list);
+static int validate_mounts(struct mount_info *info);
+
 static inline int is_root(char *p)
 {
 	return p[0] == '/' && p[1] == '\0';
@@ -59,7 +62,7 @@ int open_mount(unsigned int s_dev)
 	return -ENOENT;
 }
 
-int collect_mount_info(pid_t pid)
+int collect_mount_info(pid_t pid, bool parse)
 {
 	pr_info("Collecting mountinfo\n");
 
@@ -69,6 +72,25 @@ int collect_mount_info(pid_t pid)
 		return -1;
 	}
 
+	/*
+	 * WARN: Don't ever parse already parsed mount tree,
+	 * this will corrupt mount lists leading to weird
+	 * errors.
+	 */
+	if (parse) {
+		mntinfo_tree = mnt_build_tree(mntinfo);
+		if (!mntinfo_tree) {
+			pr_err("Building mount tree %d failed\n", getpid());
+			return -1;
+		}
+
+		if (validate_mounts(mntinfo_tree)) {
+			mntinfo_tree = NULL;
+			pr_err("Validating mount tree %d failed\n", getpid());
+			return -1;
+		}
+	}
+
 	return 0;
 }