linux-kernel - Re: [patch 2/2] splice: fix generic_file_splice

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Date:	Wed, 25 Jun 2008 15:00:41 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, hugh@...itas.com,
	nickpiggin@...oo.com.au
Subject: Re: [patch 2/2] splice: fix generic_file_splice_read() race with page invalidation

On Wed, Jun 25 2008, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@...e.cz>
> 
> If a page was invalidated during splicing from file to a pipe, then
> generic_file_splice_read() could return a short or zero count.
> 
> This manifested itself in rare I/O errors seen on nfs exported fuse
> filesystems.  This is because nfsd uses splice_direct_to_actor() to
> read files, and fuse uses invalidate_inode_pages2() to invalidate
> stale data on open.
> 
> Fix by redoing the page find/create if it was found to be truncated
> (invalidated). 
> 
> Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
> ---
>  fs/splice.c |   17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> Index: linux-2.6/fs/splice.c
> ===================================================================
> --- linux-2.6.orig/fs/splice.c	2008-06-25 08:18:51.000000000 +0200
> +++ linux-2.6/fs/splice.c	2008-06-25 11:57:33.000000000 +0200
> @@ -379,13 +379,22 @@ __generic_file_splice_read(struct file *
>  				lock_page(page);
>  
>  			/*
> -			 * page was truncated, stop here. if this isn't the
> -			 * first page, we'll just complete what we already
> -			 * added
> +			 * Page was truncated, or invalidated by the
> +			 * filesystem.  Redo the find/create, but this time the
> +			 * page is kept locked, so there's no chance of another
> +			 * race with truncate/invalidate.
>  			 */
>  			if (!page->mapping) {
>  				unlock_page(page);
> -				break;
> +				page = find_or_create_page(mapping, index,
> +						mapping_gfp_mask(mapping));
> +
> +				if (!page) {
> +					error = -ENOMEM;
> +					break;
> +				}
> +				page_cache_release(pages[page_nr]);
> +				pages[page_nr] = page;
>  			}
>  			/*
>  			 * page was already under io and is now done, great

This looks good to me, page locking is also consistent. You can add my
acked-by, I'm assuming Linus will just take it directly for 2.6.26.

-- 
Jens Axboe

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