tick: Document TICK_ONESHOT config option

[linux-flexiantxendom0-3.2.10.git] / kernel / futex.c

diff --git a/kernel/futex.c b/kernel/futex.c
index 2364c99..72efa1e 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -314,17 +314,29 @@ again:
 #endif
 
        lock_page(page_head);
+
+       /*
+        * If page_head->mapping is NULL, then it cannot be a PageAnon
+        * page; but it might be the ZERO_PAGE or in the gate area or
+        * in a special mapping (all cases which we are happy to fail);
+        * or it may have been a good file page when get_user_pages_fast
+        * found it, but truncated or holepunched or subjected to
+        * invalidate_complete_page2 before we got the page lock (also
+        * cases which we are happy to fail).  And we hold a reference,
+        * so refcount care in invalidate_complete_page's remove_mapping
+        * prevents drop_caches from setting mapping to NULL beneath us.
+        *
+        * The case we do have to guard against is when memory pressure made
+        * shmem_writepage move it from filecache to swapcache beneath us:
+        * an unlikely race, but we do need to retry for page_head->mapping.
+        */
        if (!page_head->mapping) {
+               int shmem_swizzled = PageSwapCache(page_head);
                unlock_page(page_head);
                put_page(page_head);
-               /*
-               * ZERO_PAGE pages don't have a mapping. Avoid a busy loop
-               * trying to find one. RW mapping would have COW'd (and thus
-               * have a mapping) so this page is RO and won't ever change.
-               */
-               if ((page_head == ZERO_PAGE(address)))
-                       return -EFAULT;
-               goto again;
+               if (shmem_swizzled)
+                       goto again;
+               return -EFAULT;
        }
 
        /*