Fix SMP race in truncate

PATCH In review Andrew Morton 1 participant 1 message May 5, 2002

Subsystems (2)

Memory management Page cache

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Andrew Morton

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2002-05-05 20:57 UTC #0 lore raw

PATCH 6/10 Fix SMP race in truncate

Closes a small race window: testing PageWriteback() outside the page lock introduces the possibility that page could be redirtied and have writeback started after we've inspected PageWriteback.

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mm/filemap.c renamed from mm/filemap.c~truncate-race +6 -6

@@ -201,18 +201,18 @@ static int truncate_list_pages(struct ad
 			int failed;
 
 			page_cache_get(page);
-			if (PageWriteback(page)) {
-				/*
-				 * urgggh. This function is utterly foul,
-				 * and this addition doesn't help.  Kill.
-				 */
+			failed = TestSetPageLocked(page);
+			if (!failed && PageWriteback(page)) {
+				unlock_page(page);
+				list_del(head);
+				list_add_tail(head, curr);
 				write_unlock(&mapping->page_lock);
 				wait_on_page_writeback(page);
+				page_cache_release(page);
 				unlocked = 1;
 				write_lock(&mapping->page_lock);
 				goto restart;
 			}
-			failed = TestSetPageLocked(page);
 
 			list_del(head);
 			if (!failed)