Re: [PATCH]: ufs: ufs_change_blocknr: skip truncated pages

Evgeniy Dushistov
2006-08-01T11:52:25Z

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@mail.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