RDMA/umem: Fix missing mmap_sem in get umem ODP call

Add mmap_sem lock around VMA inspection in ib_umem_odp_get().

Fixes: 0008b84e ('IB/umem: Add support to huge ODP')
Signed-off-by: Artemy Kovalyov <artemyko@mellanox.com>
Reviewed-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/umem_odp.c

@@ -321,11 +321,15 @@ int ib_umem_odp_get(struct ib_ucontext *context, struct ib_umem *umem,
 		struct vm_area_struct *vma;
 		struct hstate *h;
 
+		down_read(&mm->mmap_sem);
 		vma = find_vma(mm, ib_umem_start(umem));
-		if (!vma || !is_vm_hugetlb_page(vma))
+		if (!vma || !is_vm_hugetlb_page(vma)) {
+			up_read(&mm->mmap_sem);
 			return -EINVAL;
+		}
 		h = hstate_vma(vma);
 		umem->page_shift = huge_page_shift(h);
+		up_read(&mm->mmap_sem);
 		umem->hugetlb = 1;
 	} else {
 		umem->hugetlb = 0;