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Re-create mountpoints during restore

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runc was already re-creating mountpoints before calling CRIU to restore
a container. But mountpoints inside a bind mount were not re-created.

During initial container creation runc will mount bind mounts and then
create the necessary mountpoints for further mounts inside those bind
mounts.

If, for example, one of the bind mounts is a tmpfs and empty before
restore, CRIU will fail re-mounting all mounts because the mountpoints
in the bind mounted tmpfs no longer exist.

CRIU expects all mount points to exist as during checkpointing.

This changes runc to mount bind mounts after mountpoint creation to
ensure nested bind mounts have their mountpoints created before CRIU
does the restore.

Signed-off-by: Adrian Reber <areber@redhat.com>
This commit is contained in:
Adrian Reber
2021-02-08 13:05:54 +00:00
parent 9f1365373d
commit 705b6cc723
1 changed files with 27 additions and 0 deletions
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libcontainer/container_linux.go
+27
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@@ -1235,11 +1235,38 @@ func (c *linuxContainer) prepareCriuRestoreMounts(mounts []*configs.Mount) error
// Now go through all mounts and create the mountpoints
// if the mountpoints are not on a tmpfs, as CRIU will
// restore the complete tmpfs content from its checkpoint.
umounts := []string{}
defer func() {
for _, u := range umounts {
if e := unix.Unmount(u, unix.MNT_DETACH); e != nil {
if e != unix.EINVAL {
// Ignore EINVAL as it means 'target is not a mount point.'
// It probably has already been unmounted.
logrus.Warnf("Error during cleanup unmounting of %q (%v)", u, e)
}
}
}
}()
for _, m := range mounts {
if !isPathInPrefixList(m.Destination, tmpfs) {
if err := c.makeCriuRestoreMountpoints(m); err != nil {
return err
}
// If the mount point is a bind mount, we need to mount
// it now so that runc can create the necessary mount
// points for mounts in bind mounts.
// This also happens during initial container creation.
// Without this CRIU restore will fail
// See: https://github.com/opencontainers/runc/issues/2748
// It is also not necessary to order the mount points
// because during initial container creation mounts are
// set up in the order they are configured.
if m.Device == "bind" {
if err := unix.Mount(m.Source, m.Destination, "", unix.MS_BIND|unix.MS_REC, ""); err != nil {
return errorsf.Wrapf(err, "unable to bind mount %q to %q", m.Source, m.Destination)
}
umounts = append(umounts, m.Destination)
}
}
}
return nil