[CRIU] [PATCH] mount: restore mounts in the root mount namespace
Andrei Vagin
avagin at virtuozzo.com
Wed Feb 15 10:53:20 PST 2017
On Wed, Feb 15, 2017 at 01:26:52PM +0300, Pavel Emelyanov wrote:
> 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?
Look at this example:
The origin mount namespace has a bind mount /dev/pts/0 -> /dev/console
And one of processes has /dev/ptmx which is linked with /dev/pts/0
How we restore this construction:
1. Fork the init process into a new mount namespace (lets call it A)
2. Restore mounts
- open /dev/ptmx to bind-mount /dev/pts/0 and save the master fd in
fdstore
- bind-mount /dev/pts/0 into /dev/console
3. Create namespace which will be installed to processes
4. Restore file descriptros
- get the master fd for /dev/pts/0 from fdstore
This patch change the third step. You can see that we open a file
desctriptor in the A namespace, so if we don't intall it to one of
processes, it will be extern next time, becase criu will not be able to
find its mount by mntid.
Currently CRIU uses the A namespace to clean up remap files and clone
this namespace to restore namespaces for processes.
With this patch, the A namespace will be used as a root mount namespace
and we will clone it to create a mount namespace, which will be used to
clean up remap 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)
> >
>
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