[CRIU] Restore Failure

[Pavel Emelyanov]

On 07/19/2014 09:16 AM, Saied Kazemi wrote:
> Hi Pavel,
> 
> I have run into a problem when restoring a process that was running in a Docker container when Docker home is bind mounted from a different device.
> 
> As you know, it is possible to successfully dump and restore Docker container processes.  But when /var/lib/docker is bind mounted from a different device (e.g., mount /dev/sd3a /mnt/sd3a; mkdir /mnt/sda3/docker; mount --bind /mnt/sda3/docker /var/lib/docker), dump succeeds but restore fails.
> 
> For easier testing and debugging, I have reproduced the problem with a couple of small shell scripts that I have attached here. These are the same shell scripts that I used during external bind mount troubleshooting.  I just changed them a bit to illustrate the problem I am currently running into.  If you run ./z1.sh without the bindmount argument, everything works fine.  But if you specify bindmount, it bind mounts its root from a different device (a tmpfs in this case), dump succeeds but restore fails.  I hope it's not an error on my part.
> 
> I have been using the latest greatest criu binary from the head.  Please let me know once you've had a chance to try this.

It looks like criu constantly postpones external bind mounts. I'm trying to resolve
when we manage to break this (when I did ext-mount-map they for some reason didn't).
Meanwhile, this patch fixes it back:

diff --git a/mount.c b/mount.c
index e0e88ea..60e14d1 100644
--- a/mount.c
+++ b/mount.c
@@ -1380,9 +1380,9 @@ static bool can_mount_now(struct mount_info *mi)
 	/*
 	 * Other mounts can be mounted only if they have
 	 * the master mount (see propagate_mount) or if we
-	 * expect a plugin to help us.
+	 * expect a plugin/ext-mount-map to help us.
 	 */
-	if (mi->bind || mi->need_plugin)
+	if (mi->bind || mi->need_plugin || mi->external)
 		return true;
 
 	return false;
@@ -1415,7 +1415,7 @@ static int do_mount_one(struct mount_info *mi)
 
 	if (!mi->parent)
 		ret = do_mount_root(mi);
-	else if (!mi->bind && !mi->need_plugin)
+	else if (!mi->bind && !mi->need_plugin && !mi->external)
 		ret = do_new_mount(mi);
 	else
 		ret = do_bind_mount(mi);

Can you confirm that it fixes your problem?

Thanks,
Pavel