linux-ext4 - Re: [PATCH] resize: check s_log_groups_per

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Message-ID: <20100404021101.GD18524@thunk.org>
Date:	Sat, 3 Apr 2010 22:11:01 -0400
From:	tytso@....edu
To:	Andreas Dilger <andreas.dilger@...cle.com>
Cc:	Eric Sandeen <sandeen@...hat.com>,
	ext4 development <linux-ext4@...r.kernel.org>,
	Alessandro Polverini <alex@...bles.it>,
	Christoph Biedl <bugzilla.kernel.bpeb@...chmal.in-ulm.de>
Subject: Re: [PATCH] resize: check s_log_groups_per_flex before accessing
 flex groups

On Sun, Mar 28, 2010 at 09:14:07AM -0600, Andreas Dilger wrote:
> On 2010-03-27, at 13:32, Eric Sandeen wrote:
> >#13549, Kernel oops while online resizing of an ext4 filesystem
> >
> >if groups_per_flex < 2, sbi->s_flex_groups[] doesn't get filled out,
> >and every other access to this first tests s_log_groups_per_flex;
> >same thing needs to happen in resize or we'll wander off into
> >a null pointer.
> 
> Does it even make sense to set INCOMPAT_FLEX_BG if we only have a
> single group per flexbg?  That is just a normal filesystem then.
> That would be a separate bug in mke2fs.

Yes, it does make sense to set flex_bg in this case; it allows the
group metadata to be stored outside of a blockgroup, which is helpful
to e2fsck in some cases when it needs to relocate an inode table and
there's no contiguous free space available in the block group.

	   	      	   	 	   - Ted
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