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

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Message-ID: <20130122134400.GB28331@quack.suse.cz>
Date:	Tue, 22 Jan 2013 14:44:00 +0100
From:	Jan Kara <jack@...e.cz>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	Jan Kara <jack@...e.cz>, 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 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.

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