linux-kernel - Re: [PATCH 15/23] mm, fs: avoid page allocation beyond i

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Date:	Mon, 5 Aug 2013 10:29:17 +1000
From:	NeilBrown <neilb@...e.de>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, Dave Hansen <dave@...1.net>,
	Ning Qu <quning@...gle.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/23] mm, fs: avoid page allocation beyond i_size on
 read

On Sun,  4 Aug 2013 05:17:17 +0300 "Kirill A. Shutemov"
<kirill.shutemov@...ux.intel.com> wrote:

> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> 
> I've noticed that we allocated unneeded page for cache on read beyond
> i_size. Simple test case (I checked it on ramfs):
> 
> $ touch testfile
> $ cat testfile
> 
> It triggers 'no_cached_page' code path in do_generic_file_read().
> 
> Looks like it's regression since commit a32ea1e. Let's fix it.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: NeilBrown <neilb@...e.de>
> ---
>  mm/filemap.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 066bbff..c31d296 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1163,6 +1163,10 @@ static void do_generic_file_read(struct file *filp, loff_t *ppos,
>  		loff_t isize;
>  		unsigned long nr, ret;
>  
> +		isize = i_size_read(inode);
> +		if (!isize || index > (isize - 1) >> PAGE_CACHE_SHIFT)
> +			goto out;
> +
>  		cond_resched();
>  find_page:
>  		page = find_get_page(mapping, index);

Looks good to me.

Acked-by: NeilBrown <neilb@...e.de>

Thanks,
NeilBrown

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