rbd: prevent kernel stack blow up on rbd map

Mapping an image with a long parent chain (e.g. image foo, whose parent
is bar, whose parent is baz, etc) currently leads to a kernel stack
overflow, due to the following recursion in the reply path:

  rbd_osd_req_callback()
    rbd_obj_request_complete()
      rbd_img_obj_callback()
        rbd_img_parent_read_callback()
          rbd_obj_request_complete()
            ...

Limit the parent chain to 16 images, which is ~5K worth of stack.  When
the above recursion is eliminated, this limit can be lifted.

Fixes: http://tracker.ceph.com/issues/12538

Cc: [email protected] # 3.10+, needs backporting for < 4.2
Signed-off-by: Ilya Dryomov <[email protected]>
Reviewed-by: Josh Durgin <[email protected]>

0 files changed, 0 insertions, 0 deletions