[PATCH] unpaged: ZERO_PAGE in VM_UNPAGED

It's strange enough to be looking out for anonymous pages in VM_UNPAGED areas,
let's not insert the ZERO_PAGE there - though whether it would matter will
depend on what we decide about ZERO_PAGE refcounting.

But whereas do_anonymous_page may (exceptionally) be called on a VM_UNPAGED
area, do_no_page should never be: just BUG_ON.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 3666a4c6dd22..d1f46f4e4c8a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1812,7 +1812,16 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
         spinlock_t *ptl;
         pte_t entry;
 
-        if (write_access) {
+        /*
+         * A VM_UNPAGED vma will normally be filled with present ptes
+         * by remap_pfn_range, and never arrive here; but it might have
+         * holes, or if !VM_DONTEXPAND, mremap might have expanded it.
+         * It's weird enough handling anon pages in unpaged vmas, we do
+         * not want to worry about ZERO_PAGEs too (it may or may not
+         * matter if their counts wrap): just give them anon pages.
+         */
+
+        if (write_access || (vma->vm_flags & VM_UNPAGED)) {
                 /* Allocate our own private page. */
                 pte_unmap(page_table);
 
@@ -1887,6 +1896,7 @@ static int do_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
         int anon = 0;
 
         pte_unmap(page_table);
+        BUG_ON(vma->vm_flags & VM_UNPAGED);
 
         if (vma->vm_file) {
                 mapping = vma->vm_file->f_mapping;
@@ -1962,7 +1972,7 @@ retry:
                         inc_mm_counter(mm, anon_rss);
                         lru_cache_add_active(new_page);
                         page_add_anon_rmap(new_page, vma, address);
-                } else if (!(vma->vm_flags & VM_UNPAGED)) {
+                } else {
                         inc_mm_counter(mm, file_rss);
                         page_add_file_rmap(new_page);
                 }