hugetlb: don't use ERR_PTR with VM_FAULT* values

The current use of VM_FAULT_* codes with ERR_PTR requires us to ensure
VM_FAULT_* values will not exceed MAX_ERRNO value.  Decouple the
VM_FAULT_* values from MAX_ERRNO.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Hillf Danton <dhillf@gmail.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -1123,10 +1123,10 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
 	 */
 	chg = vma_needs_reservation(h, vma, addr);
 	if (chg < 0)
-		return ERR_PTR(-VM_FAULT_OOM);
+		return ERR_PTR(-ENOMEM);
 	if (chg)
 		if (hugepage_subpool_get_pages(spool, chg))
-			return ERR_PTR(-VM_FAULT_SIGBUS);
+			return ERR_PTR(-ENOSPC);
 
 	spin_lock(&hugetlb_lock);
 	page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve);
@@ -1136,7 +1136,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
 		page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
 		if (!page) {
 			hugepage_subpool_put_pages(spool, chg);
-			return ERR_PTR(-VM_FAULT_SIGBUS);
+			return ERR_PTR(-ENOSPC);
 		}
 	}
 
@@ -2496,6 +2496,7 @@ retry_avoidcopy:
 	new_page = alloc_huge_page(vma, address, outside_reserve);
 
 	if (IS_ERR(new_page)) {
+		long err = PTR_ERR(new_page);
 		page_cache_release(old_page);
 
 		/*
@@ -2524,7 +2525,10 @@ retry_avoidcopy:
 
 		/* Caller expects lock to be held */
 		spin_lock(&mm->page_table_lock);
-		return -PTR_ERR(new_page);
+		if (err == -ENOMEM)
+			return VM_FAULT_OOM;
+		else
+			return VM_FAULT_SIGBUS;
 	}
 
 	/*
@@ -2642,7 +2646,11 @@ retry:
 			goto out;
 		page = alloc_huge_page(vma, address, 0);
 		if (IS_ERR(page)) {
-			ret = -PTR_ERR(page);
+			ret = PTR_ERR(page);
+			if (ret == -ENOMEM)
+				ret = VM_FAULT_OOM;
+			else
+				ret = VM_FAULT_SIGBUS;
 			goto out;
 		}
 		clear_huge_page(page, address, pages_per_huge_page(h));