[PATCH] ufs: ufs_get_locked_page() race fix

As discussed earlier:
http://lkml.org/lkml/2006/6/28/136
this patch fixes such issue:

`ufs_get_locked_page' takes page from cache
after that `vmtruncate' takes page and deletes it from cache
`ufs_get_locked_page' locks page, and reports about EIO error.

Also because of find_lock_page always return valid page or NULL, we have no
need to check it if page not NULL.
Signed-off-by: Evgeniy Dushistov <dushistov@mail.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/ufs/util.c

@@ -257,6 +257,7 @@ try_again:
 		page = read_cache_page(mapping, index,
 				       (filler_t*)mapping->a_ops->readpage,
 				       NULL);
+
 		if (IS_ERR(page)) {
 			printk(KERN_ERR "ufs_change_blocknr: "
 			       "read_cache_page error: ino %lu, index: %lu\n",
@@ -266,6 +267,13 @@ try_again:
 
 		lock_page(page);
 
+		if (unlikely(page->mapping == NULL)) {
+			/* Truncate got there first */
+			unlock_page(page);
+			page_cache_release(page);
+			goto try_again;
+		}
+
 		if (!PageUptodate(page) || PageError(page)) {
 			unlock_page(page);
 			page_cache_release(page);
@@ -275,14 +283,7 @@ try_again:
 			       mapping->host->i_ino, index);
 
 			page = ERR_PTR(-EIO);
-			goto out;
-		}
 		}
-
-	if (unlikely(!page->mapping || !page_has_buffers(page))) {
-		unlock_page(page);
-		page_cache_release(page);
-		goto try_again;/*we really need these buffers*/
 	}
 out:
 	return page;