linux-ext4 - Re: [PATCH 4/4] ext4: Fix lost truncate due to race with writeback

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Date:	Mon, 26 Aug 2013 15:01:48 -0400
From:	Dave Jones <davej@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
	Zheng Liu <gnehzuil.liu@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 4/4] ext4: Fix lost truncate due to race with writeback

On Sat, Aug 17, 2013 at 10:12:27AM -0400, Theodore Ts'o wrote:
 > On Mon, Aug 05, 2013 at 03:52:24PM +0200, Jan Kara wrote:
 > > The following race can lead to a loss of i_disksize update from truncate
 > > thus resulting in a wrong inode size if the inode size isn't updated
 > > again before inode is reclaimed:
 > > 
 > > ext4_setattr()				mpage_map_and_submit_extent()
 > >   EXT4_I(inode)->i_disksize = attr->ia_size;
 > >   ...					  ...
 > > 					  disksize = ((loff_t)mpd->first_page) << PAGE_CACHE_SHIFT
 > > 					  /* False because i_size isn't
 > > 					   * updated yet */
 > > 					  if (disksize > i_size_read(inode))
 > > 					  /* True, because i_disksize is
 > > 					   * already truncated */
 > > 					  if (disksize > EXT4_I(inode)->i_disksize)
 > > 					    /* Overwrite i_disksize
 > > 					     * update from truncate */
 > > 					    ext4_update_i_disksize()
 > >   i_size_write(inode, attr->ia_size);
 > > 
 > > For other places updating i_disksize such race cannot happen because
 > > i_mutex prevents these races. Writeback is the only place where we do
 > > not hold i_mutex and we cannot grab it there because of lock ordering.
 > > 
 > > We fix the race by doing both i_disksize and i_size update in truncate
 > > atomically under i_data_sem and in mpage_map_and_submit_extent() we move
 > > the check against i_size under i_data_sem as well.
 > > 
 > > Signed-off-by: Jan Kara <jack@...e.cz>
 > 
 > Applied, thanks.

Is this queued for 3.11 ? 1k blocksize fs's are still broken in rc7.

	Dave

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