Re: [PATCH]: ufs: ufs_get_locked_patch race fix

[Andrew Morton <akpm@osdl.org>]

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.