linux-ext4 - Re: [PATCH] ext4: Make ext4_writepages() resilient to i

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Message-ID: <20130802152624.GA1121@redhat.com>
Date:	Fri, 2 Aug 2013 11:26:24 -0400
From:	Dave Jones <davej@...hat.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
	Zheng Liu <gnehzuil.liu@...il.com>
Subject: Re: [PATCH] ext4: Make ext4_writepages() resilient to i_size changes

On Fri, Aug 02, 2013 at 04:23:24PM +0200, Jan Kara wrote:
 > On Thu 01-08-13 00:42:12, Jan Kara wrote:
 > > Inode size can arbitrarily change while writeback is in progress. This
 > > can have various strange effects when we use one value of i_size for one
 > > decision during writeback and another value of i_size for a different
 > > decision during writeback. In particular a check for lblk < blocks in
 > > mpage_map_and_submit_buffers() causes problems when i_size is reduced
 > > while writeback is running because we can end up not using all blocks
 > > we've allocated. Thus these blocks are leaked and also delalloc
 > > accounting gets wrong manifesting as a warning like:
 > > 
 > > ext4_da_release_space:1333: ext4_da_release_space: ino 12, to_free 1
 > > with only 0 reserved data blocks
 > > 
 > > The problem can happen only when blocksize < pagesize because the check
 > > for size is performed only after the first iteration of the mapping
 > > loop.
 > > 
 > > Fix the problem by removing the size check from the mapping loop. We
 > > have an extent allocated so we have to use it all before checking for
 > > i_size. We may call add_page_bufs_to_extent() unnecessarily but that
 > > function won't do anything if passed block number is beyond file size.
 > > 
 > > Also to avoid future surprises like this sample inode size when
 > > starting writeback in ext4_writepages() and then use this sampled size
 > > throughout the writeback call stack.
 >   Ted, please disregard this patch. It is buggy. I'll send a better fix
 > soon.
 
I was about to post that I was seeing fsx failures on 1k filesystems
on a kernel with this patch.

Is that the same thing you're seeing ?

	Dave

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