If you are not seeing any actual I/O errors in the dmesg output, then there is probably no issue with the filesystem.
The dotdot warnings might be some edge-case being caused by the null-mounts (because the null-mount has a mount point, but its being mounted on top of a sub-directory in an underlying filesystem). If you can track down the operation that is causing message, it might just wind up being a patch to the kernel to get rid of the console warning for that particular case. If you can find a simple configuration that I can throw onto a test box to get the same error, I can track down the issue and fix it. -Matt
