1 files changed, 26 insertions, 1 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 423e0e7c2f73..d14b251a25a6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1785,7 +1785,6 @@ gotten:
         page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
         if (likely(pte_same(*page_table, orig_pte))) {
                 if (old_page) {
-                        page_remove_rmap(old_page, vma);
                         if (!PageAnon(old_page)) {
                                 dec_mm_counter(mm, file_rss);
                                 inc_mm_counter(mm, anon_rss);
@@ -1807,6 +1806,32 @@ gotten:
                 lru_cache_add_active(new_page);
                 page_add_new_anon_rmap(new_page, vma, address);
 
+                if (old_page) {
+                        /*
+                         * Only after switching the pte to the new page may
+                         * we remove the mapcount here. Otherwise another
+                         * process may come and find the rmap count decremented
+                         * before the pte is switched to the new page, and
+                         * "reuse" the old page writing into it while our pte
+                         * here still points into it and can be read by other
+                         * threads.
+                         *
+                         * The critical issue is to order this
+                         * page_remove_rmap with the ptp_clear_flush above.
+                         * Those stores are ordered by (if nothing else,)
+                         * the barrier present in the atomic_add_negative
+                         * in page_remove_rmap.
+                         *
+                         * Then the TLB flush in ptep_clear_flush ensures that
+                         * no process can access the old page before the
+                         * decremented mapcount is visible. And the old page
+                         * cannot be reused until after the decremented
+                         * mapcount is visible. So transitively, TLBs to
+                         * old page will be flushed before it can be reused.
+                         */
+                        page_remove_rmap(old_page, vma);
+                }
+
                 /* Free the old page.. */
                 new_page = old_page;
                 ret |= VM_FAULT_WRITE;