linux-ext4 - Re: [PATCH 03/12] ext4: Remove bogus wait for unwritten extents in ext4_ind_direct

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Message-ID: <20130122142221.GA1763@gmail.com>
Date:	Tue, 22 Jan 2013 22:22:21 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Dmitry Monakhov <dmonakhov@...nvz.org>, Ted Tso <tytso@....edu>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 03/12] ext4: Remove bogus wait for unwritten extents in
 ext4_ind_direct_IO

On Tue, Jan 22, 2013 at 02:44:00PM +0100, Jan Kara wrote:
> On Tue 22-01-13 15:11:24, Dmitry Monakhov wrote:
> > On Fri, 18 Jan 2013 13:00:37 +0100, Jan Kara <jack@...e.cz> wrote:
> > > When using indirect blocks there is no possibility to have any unwritten
> > > extents. So wait for them in ext4_ind_direct_IO() is just bogus.
> > But as soon as i remember indirect implementation may also be used by
> > extents based inodes 3074: ext4_ext_direct_IO
> >     /* Use the old path for reads and writes beyond i_size. */
> >     if (rw != WRITE || final_size > inode->i_size)
> >        return ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs);
> > 
> > Am I missing ?
>   Ah, that's a catch. Thanks for pointing that out! So my patch is wrong
> and that code path needs some cleaning and commenting. In particular I'm
> afraid using dioread_nolock for inodes with indirect map causes data
> exposure bugs when unlocked DIO read races with DIO write because such
> inodes don't support uninitialized extents.

Sorry, but I am still confused.  dioread_nolock is only for extent-based
file.  So when a file system without extent feature, dioread_nolock
couldn't be enabled.  It seems that we don't need to worry about
exposing stale data here.

Thanks,
                                                - Zheng
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