linux-kernel - Re: [PATCH] ext4: avoid exposure of stale data in ext4_punch

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Message-ID: <20140221002107.GB7232@thunk.org>
Date:	Thu, 20 Feb 2014 19:21:07 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	Maxim Patlasov <MPatlasov@...allels.com>, adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: avoid exposure of stale data in ext4_punch_hole()
 -v2

On Fri, Sep 27, 2013 at 06:05:17PM +0200, Jan Kara wrote:
> On Fri 27-09-13 19:54:03, Maxim Patlasov wrote:
> > While handling punch-hole fallocate, it's useless to truncate page cache
> > before removing the range from extent tree (or block map in indirect case)
> > because page cache can be re-populated (by read-ahead or read(2) or mmap-ed
> > read) immediately after truncating page cache, but before updating extent
> > tree (or block map). In that case the user will see stale data even after
> > fallocate is completed.
> > 
> > Changed in v2 (Thanks to Jan Kara):
> >  - Until the problem of data corruption resulting from pages backed by
> >    already freed blocks is fully resolved, the simple thing we can do now
> >    is to add another truncation of pagecache after punch hole is done.
>   The patch looks good. You can add:
> Reviewed-by: Jan Kara <jack@...e.cz>

I was going through old patches, and it looks like this one got
dropped.  My apologies.

As far as I can tell, the underlying problem in the VFS/MM layer
hasn't been solved yet (Jan, can you confirm?), so I've queued this
patch for the next merge window.

					- Ted
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