linux-kernel - Re: [PATCH]: ufs: ufs_change_blocknr: skip truncated pages

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Message-ID: <20060801120020.GA24263@rain>
Date:	Tue, 1 Aug 2006 16:00:20 +0400
From:	Evgeniy Dushistov <dushistov@...l.ru>
To:	Andrew Morton <akpm@...l.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH]: ufs: ufs_change_blocknr: skip truncated pages

On Tue, Aug 01, 2006 at 12:39:58AM -0700, Andrew Morton wrote:
> I'm not sure that the `goto repeat' is needed if truncate got there first,
> really - if truncate took the page down then it's now outside i_size and
> shouldn't be coming back.
> 
> If the page _can_ come back then this code is all rather problematic. 
> Because this means that the page can come back (via an extending write())
> one nanosecond after ufs_get_locked_page() returns NULL.  Won't the callers
> of ufs_get_locked_page() get confused by that?

ufs_get_locked_page is called twice in ufs code, 
one time in ufs_truncate path(we allocated last block), 
and another time when fragments are reallocated.
In ideal world in the second case on allocation/free block layer we
should not know that things like `truncate' exists, but now with
such crutch like ufs_get_locked_page we can (or should?) skip truncated pages.

Signed-off-by: Evgeniy Dushistov <dushistov@...l.ru>

---

Index: linux-2.6.18-rc2-mm1/fs/ufs/balloc.c
===================================================================
--- linux-2.6.18-rc2-mm1.orig/fs/ufs/balloc.c
+++ linux-2.6.18-rc2-mm1/fs/ufs/balloc.c
@@ -248,7 +248,7 @@ static void ufs_change_blocknr(struct in
 
 		if (likely(cur_index != index)) {
 			page = ufs_get_locked_page(mapping, index);
-			if (IS_ERR(page))
+			if (!page || IS_ERR(page)) /* it was truncated or EIO */
 				continue;
 		} else
 			page = locked_page;
Index: linux-2.6.18-rc2-mm1/fs/ufs/util.c
===================================================================
--- linux-2.6.18-rc2-mm1.orig/fs/ufs/util.c
+++ linux-2.6.18-rc2-mm1/fs/ufs/util.c
@@ -251,7 +251,6 @@ struct page *ufs_get_locked_page(struct 
 {
 	struct page *page;
 
-try_again:
 	page = find_lock_page(mapping, index);
 	if (!page) {
 		page = read_cache_page(mapping, index,
@@ -271,7 +270,8 @@ try_again:
 			/* Truncate got there first */
 			unlock_page(page);
 			page_cache_release(page);
-			goto try_again;
+			page = NULL;
+			goto out;
 		}
 
 		if (!PageUptodate(page) || PageError(page)) {

-- 
/Evgeniy

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