[PATCH] powerpc/npu-dma.c: Fix deadlock in mmio_invalidate

[Mark Hairgrove]

On Mon, 19 Feb 2018, Balbir Singh wrote:

> Good point, although I think the acquire_* function itself may be called
> from a higher layer with the mmap_sem always held. I wonder if we need
> barriers around get and put mmio_atsd_reg.

I agree with the need for memory barriers. FWIW, page tables can be
invalidated without mmap_sem being held, for example by
unmap_mapping_range.