[PATCH] x86_64: Fix a race in the free_iommu path.

[PATCH] x86_64: Fix a race in the free_iommu path.

We do this by removing a micro-optimization that tries to avoid grabbing
the iommu_bitmap_lock spinlock and using a bus-locked operation.

This still races with other simultaneous alloc_iommu or free_iommu(size
> 1) which both use bus-unlocked operations.

The end result of this race is eventually ending
up with an iommu_gart_bitmap that has bits errornously set all over,
making large contiguous iommu space allocations fail with 'PCI-DMA:
Out of IOMMU space'.

Signed-off-by: Mike Waychison <mikew@google.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>