drivers/IB,hfi1: do not se mmap_sem

This driver already uses gup_fast() and thus we can just drop the mmap_sem
protection around the pinned_vm counter. Note that the window between when
hfi1_can_pin_pages() is called and the actual counter is incremented
remains the same as mmap_sem was _only_ used for when ->pinned_vm was
touched.
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Davidlohr Bueso <dbueso@suse.det>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/hfi1/user_pages.c

@@ -91,9 +91,7 @@ bool hfi1_can_pin_pages(struct hfi1_devdata *dd, struct mm_struct *mm,
 	/* Convert to number of pages */
 	size = DIV_ROUND_UP(size, PAGE_SIZE);
 
-	down_read(&mm->mmap_sem);
 	pinned = atomic64_read(&mm->pinned_vm);
-	up_read(&mm->mmap_sem);
 
 	/* First, check the absolute limit against all pinned pages. */
 	if (pinned + npages >= ulimit && !can_lock)
@@ -111,9 +109,7 @@ int hfi1_acquire_user_pages(struct mm_struct *mm, unsigned long vaddr, size_t np
 	if (ret < 0)
 		return ret;
 
-	down_write(&mm->mmap_sem);
 	atomic64_add(ret, &mm->pinned_vm);
-	up_write(&mm->mmap_sem);
 
 	return ret;
 }
@@ -130,8 +126,6 @@ void hfi1_release_user_pages(struct mm_struct *mm, struct page **p,
 	}
 
 	if (mm) { /* during close after signal, mm can be NULL */
-		down_write(&mm->mmap_sem);
 		atomic64_sub(npages, &mm->pinned_vm);
-		up_write(&mm->mmap_sem);
 	}
 }