From: Ted Ts'o <tytso@mit.edu>
Subject: Re: [PATCH 0/5] mballoc: trivial code cleanup
Date: Mon, 7 Feb 2011 17:24:50 -0500
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To: Amir Goldstein <amir73il@gmail.com>
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On Mon, Feb 07, 2011 at 10:59:54PM +0200, Amir Goldstein wrote:
> it says alloc_sem protects against lazy init of adjacent groups
> and says nothing about protecting block group specific data structures...
> 
> what am I missing???

You're missing ext4_mb_load_buddy(), which takes grp->alloc_sem, and
which is released by ext4_mb_unload_buddy().  No, it's not the most
obvious code in the world...

					- Ted