mm: remove VM_LOCK_RMAP code

When a VMA is in an inconsistent state during setup or teardown, the worst
that can happen is that the rmap code will not be able to find the page.

The mapping is in the process of being torn down (PTEs just got
invalidated by munmap), or set up (no PTEs have been instantiated yet).

It is also impossible for the rmap code to follow a pointer to an already
freed VMA, because the rmap code holds the anon_vma->lock, which the VMA
teardown code needs to take before the VMA is removed from the anon_vma
chain.

Hence, we should not need the VM_LOCK_RMAP locking at all.

Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 12 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 28bcdc433d88..4d2fb93851ca 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -329,18 +329,6 @@ vma_address(struct page *page, struct vm_area_struct *vma)
                 /* page should be within @vma mapping range */
                 return -EFAULT;
         }
-        if (unlikely(vma->vm_flags & VM_LOCK_RMAP)) {
-                /*
-                 * This VMA is being unlinked or is not yet linked into the
-                 * VMA tree.  Do not try to follow this rmap.  This race
-                 * condition can result in page_referenced() ignoring a
-                 * reference or in try_to_unmap() failing to unmap a page.
-                 * The VMA cannot be freed under us because we hold the
-                 * anon_vma->lock, which the munmap code takes while
-                 * unlinking the anon_vmas from the VMA.
-                 */
-                return -EFAULT;
-        }
         return address;
 }