linux-ext4 - Re: [RFC 1/2] iomap: direct-io: Move inode_dio_begin before filemap_write_and_wait

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Message-ID: <20200115091925.GC31450@quack2.suse.cz>
Date:   Wed, 15 Jan 2020 10:19:25 +0100
From:   Jan Kara <jack@...e.cz>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jan Kara <jack@...e.cz>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [RFC 1/2] iomap: direct-io: Move inode_dio_begin before
 filemap_write_and_wait_range

On Tue 14-01-20 08:38:18, Christoph Hellwig wrote:
> On Tue, Jan 14, 2020 at 10:05:07AM +0100, Jan Kara wrote:
> > 
> > Well, XFS always performs buffered writeback using unwritten extents so at
> > least the immediate problem of stale data exposure ext4 has does not happen
> > there AFAICT. 
> 
> Currently XFS never uses unwritten extents when converting delalloc
> extents.

I see, it is a long time since I last looked at that part of XFS code. So
then I think XFS might be prone to the same kind of race and data exposure
as I outlined in [1]...

								Honza

[1] https://lore.kernel.org/linux-ext4/20200114094741.GC6466@quack2.suse.cz

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR