mm: fix clear_page_dirty_for_io vs fault race

[mirror_ubuntu-bionic-kernel.git] / mm / memory.c

diff --git a/mm/memory.c b/mm/memory.c
index 61d51da7e17c7e165ea69ac2383f54e2256567c9..50dd3d1f4d1832494decbe9c4b45c129817487c1 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1765,6 +1765,15 @@ gotten:
 unlock:
        pte_unmap_unlock(page_table, ptl);
        if (dirty_page) {
+               /*
+                * Yes, Virginia, this is actually required to prevent a race
+                * with clear_page_dirty_for_io() from clearing the page dirty
+                * bit after it clear all dirty ptes, but before a racing
+                * do_wp_page installs a dirty pte.
+                *
+                * do_no_page is protected similarly.
+                */
+               wait_on_page_locked(dirty_page);
                set_page_dirty_balance(dirty_page);
                put_page(dirty_page);
        }