From: Peter Zijlstra <a.p.zijlstra@chello.nl>

get_user_pages(.write=1, .force=1) can generate COW hits on read-only
shared mappings, this patch traps those as mkpage_write candidates and
fails to handle them the old way.

Cc: David Howells <dhowells@redhat.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Joel Becker <Joel.Becker@oracle.com>
Cc: Mark Fasheh <mark.fasheh@oracle.com>
Cc: Anton Altaparmakov <aia21@cantab.net>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 mm/memory.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff -puN mm/memory.c~add-page_mkwrite-vm_operations-method-fix mm/memory.c
--- a/mm/memory.c~add-page_mkwrite-vm_operations-method-fix
+++ a/mm/memory.c
@@ -1463,7 +1463,8 @@ static int do_wp_page(struct mm_struct *
 	if (!old_page)
 		goto gotten;
 
-	if (unlikely(vma->vm_flags & VM_SHARED)) {
+	if (unlikely((vma->vm_flags & (VM_SHARED|VM_WRITE)) ==
+				(VM_SHARED|VM_WRITE))) {
 		if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
 			/*
 			 * Notify the address space that the page is about to
_