diff -druNp --no-dereference linux-libre-3.2.82-gnu1/include/linux/mm.h linux-libre-3.2.83-gnu1/include/linux/mm.h
--- linux-libre-3.2.82-gnu1/include/linux/mm.h	2016-08-22 17:37:20.000000000 -0400
+++ linux-libre-3.2.83-gnu1/include/linux/mm.h	2016-10-20 18:41:00.000000000 -0400
@@ -1527,6 +1527,7 @@ struct page *follow_page(struct vm_area_
 #define FOLL_MLOCK	0x40	/* mark page as mlocked */
 #define FOLL_SPLIT	0x80	/* don't return transhuge pages, split them */
 #define FOLL_HWPOISON	0x100	/* check page is hwpoisoned */
+#define FOLL_COW	0x4000	/* internal GUP flag */
 
 typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
 			void *data);
diff -druNp --no-dereference linux-libre-3.2.82-gnu1/Makefile linux-libre-3.2.83-gnu1/Makefile
--- linux-libre-3.2.82-gnu1/Makefile	2016-08-23 16:22:15.000000000 -0400
+++ linux-libre-3.2.83-gnu1/Makefile	2016-10-21 11:05:09.000000000 -0400
@@ -1,6 +1,6 @@
 VERSION = 3
 PATCHLEVEL = 2
-SUBLEVEL = 82
+SUBLEVEL = 83
 EXTRAVERSION =-gnu1
 NAME = Saber-toothed Squirrel
 
diff -druNp --no-dereference linux-libre-3.2.82-gnu1/mm/memory.c linux-libre-3.2.83-gnu1/mm/memory.c
--- linux-libre-3.2.82-gnu1/mm/memory.c	2016-08-22 17:37:20.000000000 -0400
+++ linux-libre-3.2.83-gnu1/mm/memory.c	2016-10-20 18:41:00.000000000 -0400
@@ -1427,6 +1427,24 @@ int zap_vma_ptes(struct vm_area_struct *
 }
 EXPORT_SYMBOL_GPL(zap_vma_ptes);
 
+static inline bool can_follow_write_pte(pte_t pte, struct page *page,
+					unsigned int flags)
+{
+	if (pte_write(pte))
+		return true;
+
+	/*
+	 * Make sure that we are really following CoWed page. We do not really
+	 * have to care about exclusiveness of the page because we only want
+	 * to ensure that once COWed page hasn't disappeared in the meantime
+	 * or it hasn't been merged to a KSM page.
+	 */
+	if ((flags & FOLL_FORCE) && (flags & FOLL_COW))
+		return page && PageAnon(page) && !PageKsm(page);
+
+	return false;
+}
+
 /**
  * follow_page - look up a page descriptor from a user-virtual address
  * @vma: vm_area_struct mapping @address
@@ -1509,10 +1527,13 @@ split_fallthrough:
 	pte = *ptep;
 	if (!pte_present(pte))
 		goto no_page;
-	if ((flags & FOLL_WRITE) && !pte_write(pte))
-		goto unlock;
 
 	page = vm_normal_page(vma, address, pte);
+	if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, page, flags)) {
+		pte_unmap_unlock(ptep, ptl);
+		return NULL;
+	}
+
 	if (unlikely(!page)) {
 		if ((flags & FOLL_DUMP) ||
 		    !is_zero_pfn(pte_pfn(pte)))
@@ -1555,7 +1576,7 @@ split_fallthrough:
 			unlock_page(page);
 		}
 	}
-unlock:
+
 	pte_unmap_unlock(ptep, ptl);
 out:
 	return page;
@@ -1789,17 +1810,13 @@ int __get_user_pages(struct task_struct
 				 * The VM_FAULT_WRITE bit tells us that
 				 * do_wp_page has broken COW when necessary,
 				 * even if maybe_mkwrite decided not to set
-				 * pte_write. We can thus safely do subsequent
-				 * page lookups as if they were reads. But only
-				 * do so when looping for pte_write is futile:
-				 * in some cases userspace may also be wanting
-				 * to write to the gotten user page, which a
-				 * read fault here might prevent (a readonly
-				 * page might get reCOWed by userspace write).
+				 * pte_write. We cannot simply drop FOLL_WRITE
+				 * here because the COWed page might be gone by
+				 * the time we do the subsequent page lookups.
 				 */
 				if ((ret & VM_FAULT_WRITE) &&
 				    !(vma->vm_flags & VM_WRITE))
-					foll_flags &= ~FOLL_WRITE;
+					foll_flags |= FOLL_COW;
 
 				cond_resched();
 			}
