From: Pekka Enberg <penberg@cs.helsinki.fi>

As pointed out by Nick Piggin, __revoke_break_cow() only needs to do
down_read() and we must use vma_pages() for get_user_pages().

Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/revoke.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff -puN fs/revoke.c~revoke-core-code-break-cow-fixes fs/revoke.c
--- a/fs/revoke.c~revoke-core-code-break-cow-fixes
+++ a/fs/revoke.c
@@ -185,7 +185,7 @@ static int __revoke_break_cow(struct tas
 	struct vm_area_struct *vma;
 	int err = 0;
 
-	down_write(&mm->mmap_sem);
+	down_read(&mm->mmap_sem);
 	for (vma = mm->mmap; vma != NULL; vma = vma->vm_next) {
 		int ret;
 
@@ -196,14 +196,13 @@ static int __revoke_break_cow(struct tas
 			continue;
 
 		ret = get_user_pages(tsk, tsk->mm, vma->vm_start,
-				     vma->vm_end-vma->vm_start, 1, 1, NULL,
-				     NULL);
+				     vma_pages(vma), 1, 1, NULL, NULL);
 		if (ret < 0) {
 			err = ret;
 			break;
 		}
 	}
-	up_write(&mm->mmap_sem);
+	up_read(&mm->mmap_sem);
 	return err;
 }
 
_