fbdev: update after backlight argument change

[safe/jmp/linux-2.6] / mm / vmscan.c

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 87d3409..f05527b 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -378,17 +378,42 @@ static pageout_t pageout(struct page *page, struct address_space *mapping)
        return PAGE_CLEAN;
 }
 
+/*
+ * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
+ * someone else has a ref on the page, abort and return 0.  If it was
+ * successfully detached, return 1.  Assumes the caller has a single ref on
+ * this page.
+ */
 int remove_mapping(struct address_space *mapping, struct page *page)
 {
        BUG_ON(!PageLocked(page));
        BUG_ON(mapping != page_mapping(page));
 
        write_lock_irq(&mapping->tree_lock);
-
        /*
-        * The non-racy check for busy page.  It is critical to check
-        * PageDirty _after_ making sure that the page is freeable and
-        * not in use by anybody.       (pagecache + us == 2)
+        * The non racy check for a busy page.
+        *
+        * Must be careful with the order of the tests. When someone has
+        * a ref to the page, it may be possible that they dirty it then
+        * drop the reference. So if PageDirty is tested before page_count
+        * here, then the following race may occur:
+        *
+        * get_user_pages(&page);
+        * [user mapping goes away]
+        * write_to(page);
+        *                              !PageDirty(page)    [good]
+        * SetPageDirty(page);
+        * put_page(page);
+        *                              !page_count(page)   [good, discard it]
+        *
+        * [oops, our write_to data is lost]
+        *
+        * Reversing the order of the tests ensures such a situation cannot
+        * escape unnoticed. The smp_rmb is needed to ensure the page->flags
+        * load is not satisfied before that of page->_count.
+        *
+        * Note that if SetPageDirty is always performed via set_page_dirty,
+        * and thus under tree_lock, then this ordering is not required.
         */
        if (unlikely(page_count(page) != 2))
                goto cannot_free;
@@ -1034,7 +1059,7 @@ unsigned long try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
 
                /* Take a nap, wait for some writeback to complete */
                if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
-                       blk_congestion_wait(WRITE, HZ/10);
+                       congestion_wait(WRITE, HZ/10);
        }
        /* top priority shrink_caches still had more to do? don't OOM, then */
        if (!sc.all_unreclaimable)
@@ -1189,7 +1214,7 @@ scan:
                 * another pass across the zones.
                 */
                if (total_scanned && priority < DEF_PRIORITY - 2)
-                       blk_congestion_wait(WRITE, HZ/10);
+                       congestion_wait(WRITE, HZ/10);
 
                /*
                 * We do this so kswapd doesn't build up large priorities for
@@ -1433,7 +1458,7 @@ unsigned long shrink_all_memory(unsigned long nr_pages)
                                goto out;
 
                        if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
-                               blk_congestion_wait(WRITE, HZ / 10);
+                               congestion_wait(WRITE, HZ / 10);
                }
 
                lru_pages = 0;