1 files changed, 52 insertions, 54 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 8d9b19f239c..1d2fc89ca56 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -21,6 +21,7 @@
 #include <linux/writeback.h>
 #include <linux/init.h>
 #include <linux/backing-dev.h>
+#include <linux/task_io_accounting_ops.h>
 #include <linux/blkdev.h>
 #include <linux/mpage.h>
 #include <linux/rmap.h>
@@ -761,23 +762,24 @@ int __set_page_dirty_nobuffers(struct page *page)
 		struct address_space *mapping = page_mapping(page);
 		struct address_space *mapping2;
 
-		if (mapping) {
-			write_lock_irq(&mapping->tree_lock);
-			mapping2 = page_mapping(page);
-			if (mapping2) { /* Race with truncate? */
-				BUG_ON(mapping2 != mapping);
-				if (mapping_cap_account_dirty(mapping))
-					__inc_zone_page_state(page,
-								NR_FILE_DIRTY);
-				radix_tree_tag_set(&mapping->page_tree,
-					page_index(page), PAGECACHE_TAG_DIRTY);
-			}
-			write_unlock_irq(&mapping->tree_lock);
-			if (mapping->host) {
-				/* !PageAnon && !swapper_space */
-				__mark_inode_dirty(mapping->host,
-							I_DIRTY_PAGES);
+		if (!mapping)
+			return 1;
+
+		write_lock_irq(&mapping->tree_lock);
+		mapping2 = page_mapping(page);
+		if (mapping2) { /* Race with truncate? */
+			BUG_ON(mapping2 != mapping);
+			if (mapping_cap_account_dirty(mapping)) {
+				__inc_zone_page_state(page, NR_FILE_DIRTY);
+				task_io_account_write(PAGE_CACHE_SIZE);
 			}
+			radix_tree_tag_set(&mapping->page_tree,
+				page_index(page), PAGECACHE_TAG_DIRTY);
+		}
+		write_unlock_irq(&mapping->tree_lock);
+		if (mapping->host) {
+			/* !PageAnon && !swapper_space */
+			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 		}
 		return 1;
 	}
@@ -843,39 +845,6 @@ int set_page_dirty_lock(struct page *page)
 EXPORT_SYMBOL(set_page_dirty_lock);
 
 /*
- * Clear a page's dirty flag, while caring for dirty memory accounting. 
- * Returns true if the page was previously dirty.
- */
-int test_clear_page_dirty(struct page *page)
-{
-	struct address_space *mapping = page_mapping(page);
-	unsigned long flags;
-
-	if (mapping) {
-		write_lock_irqsave(&mapping->tree_lock, flags);
-		if (TestClearPageDirty(page)) {
-			radix_tree_tag_clear(&mapping->page_tree,
-						page_index(page),
-						PAGECACHE_TAG_DIRTY);
-			write_unlock_irqrestore(&mapping->tree_lock, flags);
-			/*
-			 * We can continue to use `mapping' here because the
-			 * page is locked, which pins the address_space
-			 */
-			if (mapping_cap_account_dirty(mapping)) {
-				page_mkclean(page);
-				dec_zone_page_state(page, NR_FILE_DIRTY);
-			}
-			return 1;
-		}
-		write_unlock_irqrestore(&mapping->tree_lock, flags);
-		return 0;
-	}
-	return TestClearPageDirty(page);
-}
-EXPORT_SYMBOL(test_clear_page_dirty);
-
-/*
  * Clear a page's dirty flag, while caring for dirty memory accounting.
  * Returns true if the page was previously dirty.
  *
@@ -893,12 +862,41 @@ int clear_page_dirty_for_io(struct page *page)
 {
 	struct address_space *mapping = page_mapping(page);
 
-	if (mapping) {
+	if (mapping && mapping_cap_account_dirty(mapping)) {
+		/*
+		 * Yes, Virginia, this is indeed insane.
+		 *
+		 * We use this sequence to make sure that
+		 *  (a) we account for dirty stats properly
+		 *  (b) we tell the low-level filesystem to
+		 *      mark the whole page dirty if it was
+		 *      dirty in a pagetable. Only to then
+		 *  (c) clean the page again and return 1 to
+		 *      cause the writeback.
+		 *
+		 * This way we avoid all nasty races with the
+		 * dirty bit in multiple places and clearing
+		 * them concurrently from different threads.
+		 *
+		 * Note! Normally the "set_page_dirty(page)"
+		 * has no effect on the actual dirty bit - since
+		 * that will already usually be set. But we
+		 * need the side effects, and it can help us
+		 * avoid races.
+		 *
+		 * We basically use the page "master dirty bit"
+		 * as a serialization point for all the different
+		 * threads doing their things.
+		 *
+		 * FIXME! We still have a race here: if somebody
+		 * adds the page back to the page tables in
+		 * between the "page_mkclean()" and the "TestClearPageDirty()",
+		 * we might have it mapped without the dirty bit set.
+		 */
+		if (page_mkclean(page))
+			set_page_dirty(page);
 		if (TestClearPageDirty(page)) {
-			if (mapping_cap_account_dirty(mapping)) {
-				page_mkclean(page);
-				dec_zone_page_state(page, NR_FILE_DIRTY);
-			}
+			dec_zone_page_state(page, NR_FILE_DIRTY);
 			return 1;
 		}
 		return 0;