linux-ext4 - Re: [PATCH] fix header check in ext4_ext_search

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Date:	Mon, 09 Mar 2009 10:53:10 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Theodore Tso <tytso@....edu>
CC:	ext4 development <linux-ext4@...r.kernel.org>,
	David Dindorp <ddi@...ex.dk>
Subject: Re: [PATCH] fix header check in ext4_ext_search_right() for deep
 extent trees.

Theodore Tso wrote:
> On Fri, Mar 06, 2009 at 02:50:51PM -0600, Eric Sandeen wrote:
>> This should resolve kernel.org bugzilla 12821
>>
>> I've not actually crafted a workload to exercise this code; 
>> this is from inspection...
> 
> Hmm, so I've been trying to create a test case, but the test cases
> I've created (which e2fsck say are fine) aren't causing complaints by
> the kernel.
> 
> Please see:
> 
>        http://master.kernel.org/~tytso/deep-tree/
> 
> deep-tree.img.gz contains an extent tree of depth 3, and
> deep-tree-2.img.gz contains an extent tree of depth 4....
> 
> 		   	       	      - Ted

I've had no trouble creating a deep tree, but I have had trouble making
it actually exercise the code in that loop.

I think the initial ext4_ext_find_extent() needs to land us in just the
right place such that the search_right must traverse back up & back down
the tree to get the nearest right allocation... I haven't sorted that
out yet.

I'd feel better w/ a testcase to demonstrate correctness too, but I'm
99.9% sure that the fix is correct by inspection, and would rather see
it get into .29 sooner than later unless you have strong misgivings.

-Eric
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