linux-ext4 - Re: [PATCH] ext4: fix partial cluster handling for bigalloc file systems

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Date:	Thu, 13 Mar 2014 23:35:11 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Eric Whitney <enwlinux@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: fix partial cluster handling for bigalloc file
 systems

On Wed, Mar 12, 2014 at 05:27:36PM -0400, Eric Whitney wrote:
> Commit 9cb00419fa, which enables hole punching for bigalloc file
> systems, exposed a bug introduced by commit 6ae06ff51e in an earlier
> release.  When run on a bigalloc file system, xfstests generic/013, 068,
> 075, 083, 091, 100, 112, 127, 263, 269, and 270 fail with e2fsck errors
> or cause kernel error messages indicating that previously freed blocks
> are being freed again.
> 
> The latter commit optimizes the selection of the starting extent in
> ext4_ext_rm_leaf() when hole punching by beginning with the extent
> supplied in the path argument rather than with the last extent in the
> leaf node (as is still done when truncating).  However, the code in
> rm_leaf that initially sets partial_cluster to track cluster sharing on
> extent boundaries is only guaranteed to run if rm_leaf starts with the
> last node in the leaf.  Consequently, partial_cluster is not correctly
> initialized when hole punching, and a cluster on the boundary of a
> punched region that should be retained may instead be deallocated.
> 
> Signed-off-by: Eric Whitney <enwlinux@...il.com>

Thanks, applied.

					- Ted
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