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

[Pavel Emelyanov]

On 02/15/2017 12:49 AM, Andrei Vagin wrote:
> 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.

I don't get this. Would you describe the problem in more detail?

> 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)
>