linux-ext4 - Re: Hole punching and mmap races

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Message-ID: <20120518101210.GX25351@dastard>
Date:	Fri, 18 May 2012 20:12:10 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-fsdevel@...r.kernel.org, xfs@....sgi.com,
	linux-ext4@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	linux-mm@...ck.org
Subject: Re: Hole punching and mmap races

On Fri, May 18, 2012 at 01:28:29AM +0200, Jan Kara wrote:
> On Thu 17-05-12 17:43:08, Dave Chinner wrote:
> > On Wed, May 16, 2012 at 03:04:45PM +0200, Jan Kara wrote:
> > > On Wed 16-05-12 12:14:23, Dave Chinner wrote:
> > IIRC, it's a rare case (that I consider insane, BTW):  read from a
> > file with into a buffer that is a mmap()d region of the same file
> > that has not been faulted in yet.....
>   With punch hole, the race is less insane - just punching hole in the area
> which is accessed via mmap could race in a bad way AFAICS.

Seems the simple answer to me is to prevent page faults while hole
punching, then....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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