rbd: prevent kernel stack blow up on rbd map
commit 6d69bb53 upstream. 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/12538Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Reviewed-by: Josh Durgin <jdurgin@redhat.com> [idryomov@gmail.com: backport to 3.10: rbd_dev->opts, context] Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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