mm: fix PageUptodate data race

[mirror_ubuntu-zesty-kernel.git] / include / linux / page-flags.h

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 209d3a47f50f24b5ccbf29c6b3dd965ebb79d2d8..bbad43fb8181001b43ef1c8de406173138d118e0 100644 (file)
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -131,16 +131,52 @@
 #define ClearPageReferenced(page)      clear_bit(PG_referenced, &(page)->flags)
 #define TestClearPageReferenced(page) test_and_clear_bit(PG_referenced, &(page)->flags)
 
-#define PageUptodate(page)     test_bit(PG_uptodate, &(page)->flags)
+static inline int PageUptodate(struct page *page)
+{
+       int ret = test_bit(PG_uptodate, &(page)->flags);
+
+       /*
+        * Must ensure that the data we read out of the page is loaded
+        * _after_ we've loaded page->flags to check for PageUptodate.
+        * We can skip the barrier if the page is not uptodate, because
+        * we wouldn't be reading anything from it.
+        *
+        * See SetPageUptodate() for the other side of the story.
+        */
+       if (ret)
+               smp_rmb();
+
+       return ret;
+}
+
+static inline void __SetPageUptodate(struct page *page)
+{
+       smp_wmb();
+       __set_bit(PG_uptodate, &(page)->flags);
 #ifdef CONFIG_S390
+       page_clear_dirty(page);
+#endif
+}
+
 static inline void SetPageUptodate(struct page *page)
 {
+#ifdef CONFIG_S390
        if (!test_and_set_bit(PG_uptodate, &page->flags))
                page_clear_dirty(page);
-}
 #else
-#define SetPageUptodate(page)  set_bit(PG_uptodate, &(page)->flags)
+       /*
+        * Memory barrier must be issued before setting the PG_uptodate bit,
+        * so that all previous stores issued in order to bring the page
+        * uptodate are actually visible before PageUptodate becomes true.
+        *
+        * s390 doesn't need an explicit smp_wmb here because the test and
+        * set bit already provides full barriers.
+        */
+       smp_wmb();
+       set_bit(PG_uptodate, &(page)->flags);
 #endif
+}
+
 #define ClearPageUptodate(page)        clear_bit(PG_uptodate, &(page)->flags)
 
 #define PageDirty(page)                test_bit(PG_dirty, &(page)->flags)