real-time device BUG

[Ross Zwisler]

On Fri, Jan 29, 2016 at 04:05:31PM -0700, Ross Zwisler wrote:
> Today I was trying to get real-time devices working with XFS, and both a
> manual pwrite() to a real-time device and xfs_rtcp end up with a lockdep spat
> followed by a kernel BUG.  This behavior is consistent between kernel versions
> v4.4 and v4.5-rc1.  I initially found this using some pmem block devices, but
> it also happens with BRD.

This also happens with an mmap on the real-time file followed by a write.
Essentially I think that any path that tries to allocate a block for the real
time file his this same BUG.