[PATCH] mm: mremap correct rmap accounting

Nick Piggin points out that page accounting on MIPS multiple ZERO_PAGEs
is not maintained by its move_pte, and could lead to freeing a ZERO_PAGE.

Instead of complicating that move_pte, just forget the minor optimization
when mremapping, and change the one thing which needed it for correctness
- filemap_xip use ZERO_PAGE(0) throughout instead of according to address.

[ "There is no block device driver one could use for XIP on mips
   platforms" - Carsten Otte ]

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Andrew Morton <akpm@osdl.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 2 insertions, 3 deletions

diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index 45b3553865c..9dd9fbb7513 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -183,7 +183,7 @@ __xip_unmap (struct address_space * mapping,
                 address = vma->vm_start +
                         ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
                 BUG_ON(address < vma->vm_start || address >= vma->vm_end);
-                page = ZERO_PAGE(address);
+                page = ZERO_PAGE(0);
                 pte = page_check_address(page, mm, address, &ptl);
                 if (pte) {
                         /* Nuke the page table entry. */
@@ -246,7 +246,7 @@ xip_file_nopage(struct vm_area_struct * area,
                 __xip_unmap(mapping, pgoff);
         } else {
                 /* not shared and writable, use ZERO_PAGE() */
-                page = ZERO_PAGE(address);
+                page = ZERO_PAGE(0);
         }
 
 out:
diff --git a/mm/mremap.c b/mm/mremap.c
index 9c769fa29f3..5d4bd4f95b8 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -105,7 +105,6 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
                 if (pte_none(*old_pte))
                         continue;
                 pte = ptep_clear_flush(vma, old_addr, old_pte);
-                /* ZERO_PAGE can be dependant on virtual addr */
                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
                 set_pte_at(mm, new_addr, new_pte, pte);
         }