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Re: [PATCH 3/4] fs: Remove i_size check from do_fallocate

To: Theodore Ts'o <tytso@xxxxxxx>
Subject: Re: [PATCH 3/4] fs: Remove i_size check from do_fallocate
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 14 Apr 2014 09:39:58 +1000
Cc: Lukas Czerner <lczerner@xxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, ceph-devel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140412135906.GC13837@xxxxxxxxx>
References: <1397242665-2183-1-git-send-email-lczerner@xxxxxxxxxx> <1397242665-2183-3-git-send-email-lczerner@xxxxxxxxxx> <20140412135906.GC13837@xxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Sat, Apr 12, 2014 at 09:59:06AM -0400, Theodore Ts'o wrote:
> On Fri, Apr 11, 2014 at 08:57:44PM +0200, Lukas Czerner wrote:
> > Currently in do_fallocate in collapse range case we're checking whether
> > offset + len is not bigger than i_size. However there is nothing which
> > would prevent i_size from changing so the check is pointless. It should
> > be done in the file system itself and the file system needs to make sure
> > that i_size is not going to change.
> > 
> > As it is now we can easily crash kernel by having two processes doing
> > truncate and fallocate collapse range at the same time. This can be
> > reproduced on ext4 and it is theoretically possible on xfs even though I
> > was not able to trigger it with this simple test.
> > 
> > This commit removes the check from do_fallocate and adds it to the file
> > system.
> > 
> > Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> > ---
> >  fs/ext4/extents.c | 11 +++++++++--
> >  fs/open.c         |  8 --------
> >  fs/xfs/xfs_file.c | 10 +++++++++-
> >  3 files changed, 18 insertions(+), 11 deletions(-)
> 
> Looks good to me.  Do the xfs folks mind if I carry this in the ext4
> tree and push it to Linus shortly after -rc1?  If so, please send me
> an ack'ed by.

No, go ahead. I was going to do the same thing, anyway, if nobody
else beat me to it...

Acked-by: Dave Chinner <david@xxxxxxxxxxxxx>

Cheers,

Dave
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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