Re: [PATCH]: ufs: ufs_get_locked_patch race fix

Andrew Morton
2006-08-01T06:03:00Z

On Mon, 31 Jul 2006 16:57:02 +0400
Evgeniy Dushistov <dushistov@mail.ru> wrote:

> 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 check it if page not NULL.
>
> Signed-off-by: Evgeniy Dushistov <dushistov@mail.ru>
>
>
> ---
>
>
> 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
> @@ -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 != mapping ||
> + page->index != index)) {
> + unlock_page(page);
> + page_cache_release(page);
> + goto try_again;
> + }
> +
> if (!PageUptodate(page) || PageError(page)) {
> unlock_page(page);
> page_cache_release(page);

Looks good to me.

Is there any need to be checking ->index? Normally we simply use the
sequence:

lock_page(page);
if (page->mapping == NULL)
/* truncate got there first */

to handle this case.