[CRIU] [PATCH] mount: restore mounts in the root mount namespace

[Andrei Vagin]

From: Andrei Vagin <avagin at virtuozzo.com>

Currently mounts are restored in a mount namespace, then
this namespace is cloned to create mount namespaces for
processes and finaly the first namespace is destroyed after
cleaning remap files.

But it doesn't work in a case, when we have to open file
descriptores to restore mounts (e g to restore bind-mount
pty slaves), because on the next iteration criu will not
find mounts for this files.

In this patch the first namespace is restored as the root
mount namespace and we clone the first namespace to create
a namespace whichc is used to clean remap files.

$ ./zdtm.py run -t zdtm/static/pty-console --iter 5
====================== Run zdtm/static/pty-console in ns =======================
Start test
Test is SUID
./pty-console --pidfile=pty-console.pid --outfile=pty-console.out
Run criu dump
Run criu restore
Run criu dump
=[log]=> dump/zdtm/static/pty-console/36/2/dump.log
------------------------ grep Error ------------------------
(00.106521) Error (criu/files-reg.c:1132): Can't lookup mount=563 for fd=4 path=/ptmx
(00.106585) Error (criu/cr-dump.c:1325): Dump files (pid: 70) failed with -1
(00.129041) Error (criu/cr-dump.c:1674): Dumping FAILED.
------------------------ ERROR OVER ------------------------

Signed-off-by: Andrei Vagin <avagin at virtuozzo.com>
---
 criu/cr-restore.c       | 21 +++++++++++++++++----
 criu/include/restorer.h |  5 +++++
 criu/mount.c            | 32 +++++++++++++++++++++++++++-----
 3 files changed, 49 insertions(+), 9 deletions(-)

diff --git a/criu/cr-restore.c b/criu/cr-restore.c
index d75aa0d..e20036b 100644
--- a/criu/cr-restore.c
+++ b/criu/cr-restore.c
@@ -1431,6 +1431,9 @@ static int restore_task_with_children(void *_arg)
 		if (prepare_namespace(current, ca->clone_flags))
 			goto err;
 
+		if (restore_finish_stage(task_entries, CR_STATE_POST_RESTORE_NS) < 0)
+			goto err;
+
 		if (root_prepare_shared())
 			goto err;
 
@@ -1494,6 +1497,7 @@ static inline int stage_participants(int next_stage)
 	case CR_STATE_FAIL:
 		return 0;
 	case CR_STATE_RESTORE_NS:
+	case CR_STATE_POST_RESTORE_NS:
 	case CR_STATE_RESTORE_SHARED:
 		return 1;
 	case CR_STATE_FORKING:
@@ -1850,16 +1854,25 @@ static int restore_root_task(struct pstree_item *init)
 	if (ret)
 		goto out_kill;
 
+	ret = run_scripts(ACT_SETUP_NS);
+	if (ret)
+		goto out_kill;
+
+	ret = restore_switch_stage(CR_STATE_POST_RESTORE_NS);
+	if (ret < 0)
+		goto out_kill;
+
+	pr_info("Wait until namespaces are created\n");
+	ret = restore_wait_inprogress_tasks();
+	if (ret)
+		goto out_kill;
+
 	if (root_ns_mask & CLONE_NEWNS) {
 		mnt_ns_fd = open_proc(init->pid->real, "ns/mnt");
 		if (mnt_ns_fd < 0)
 			goto out_kill;
 	}
 
-	ret = run_scripts(ACT_SETUP_NS);
-	if (ret)
-		goto out_kill;
-
 	if (opts.empty_ns & CLONE_NEWNET) {
 		/*
 		 * Local TCP connections were locked by network_lock_internal()
diff --git a/criu/include/restorer.h b/criu/include/restorer.h
index 23c7e24..7c65538 100644
--- a/criu/include/restorer.h
+++ b/criu/include/restorer.h
@@ -203,6 +203,11 @@ static inline unsigned long restorer_stack(struct restore_mem_zone *mz)
 enum {
 	CR_STATE_FAIL		= -1,
 	CR_STATE_RESTORE_NS	= 0, /* is used for executing "setup-namespace" scripts */
+	/*
+	 * Need to wait a mount namespace which
+	 * will be used to clean up remap files.
+	 */
+	CR_STATE_POST_RESTORE_NS,
 	CR_STATE_RESTORE_SHARED,
 	CR_STATE_FORKING,
 	CR_STATE_RESTORE,
diff --git a/criu/mount.c b/criu/mount.c
index 8f66b4e..013b17e 100644
--- a/criu/mount.c
+++ b/criu/mount.c
@@ -2948,17 +2948,39 @@ int prepare_mnt_ns(void)
 			goto err;
 		}
 
+		if (nsid->type == NS_ROOT) {
+			int fd;
+
+			/*
+			 * We need to create a mount namespace which will be
+			 * used to clean up remap files
+			 * (depopulate_roots_yard).  The namespace where mounts
+			 * was restored has to be restored as a root mount
+			 * namespace, because there are file descriptors
+			 * linked with it (e.g. to bind-mount slave pty-s).
+			 */
+			fd = open_proc(PROC_SELF, "ns/mnt");
+			if (fd < 0)
+				goto err;
+			if (setns(rst, CLONE_NEWNS)) {
+				pr_perror("Can't restore mntns back");
+				goto err;
+			}
+			nsid->mnt.ns_fd = rst;
+			rst = fd;
+		} else {
+			/* Pin one with a file descriptor */
+			nsid->mnt.ns_fd = open_proc(PROC_SELF, "ns/mnt");
+			if (nsid->mnt.ns_fd < 0)
+				goto err;
+		}
+
 		/* Set its root */
 		path[0] = '/';
 		print_ns_root(nsid, 0, path + 1, sizeof(path) - 1);
 		if (cr_pivot_root(path))
 			goto err;
 
-		/* Pin one with a file descriptor */
-		nsid->mnt.ns_fd = open_proc(PROC_SELF, "ns/mnt");
-		if (nsid->mnt.ns_fd < 0)
-			goto err;
-
 		/* root_fd is used to restore file mappings */
 		nsid->mnt.root_fd = open_proc(PROC_SELF, "root");
 		if (nsid->mnt.root_fd < 0)
-- 
2.7.4