From: Zwane Mwaikambo <zwane@linuxpower.ca>

The code appears to be able to add too many blocks back to
sbinfo->free_blocks in the failure path. We first do;

len = vma->vm_end - vma->vm_start;
sbinfo->free_blocks -= len;

but then later do;
len = (vma->vm_end - vma->vma_start) + (vma->vm_pgoff << HPAGE_SHIFT)

error:
sbinfo->free_blocks += len;