mm: fix apply_to_existing_page_range()

In the case of apply_to_existing_page_range(), apply_to_pte_range() is
reached with 'create' set to false.  When !create, the loop over the PTE
page table is broken.

apply_to_pte_range() will only move to the next PTE entry if 'create' is
true or if the current entry is not pte_none().

This means that the user of apply_to_existing_page_range() will not have
'fn' called for any entries after the first pte_none() in the PTE page
table.

Fix the loop logic in apply_to_pte_range().

There are no known runtime issues from this, but the fix is trivial enough
for stable@ even without a known buggy user. 

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kirill A. Shutemov <[email protected]>
Fixes: be1db47 ("mm/memory.c: add apply_to_existing_page_range() helper")
Cc: Daniel Axtens <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: kiryl

mm/memory.c

@@ -2938,11 +2938,11 @@ static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
 	if (fn) {
 		do {
 			if (create || !pte_none(ptep_get(pte))) {
-				err = fn(pte++, addr, data);
+				err = fn(pte, addr, data);
 				if (err)
 					break;
 			}
-		} while (addr += PAGE_SIZE, addr != end);
+		} while (pte++, addr += PAGE_SIZE, addr != end);
 	}
 	*mask |= PGTBL_PTE_MODIFIED;