From: Andreas Schlick <schlick@lavabit.com>
Subject: [PATCH 0/2] Fix wrong name_len and file_type in intermediate htree nodes
Date: Sun, 30 Aug 2009 16:56:40 +0200
Message-ID: <200908301656.40866.schlick@lavabit.com>
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To: Ext4 Developers List <linux-ext4@vger.kernel.org>
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Hello,

while testing the dirshrink patch, I found that sometimes intermediate htree 
nodes end up with their fake_dirent's name_len and file_type not being zero. 
e2fsck will then consider the htree to be corrupted as it doesn't recognise 
that these blocks contain dx_nodes. 

As far as I understand it, this happens sometimes when ext4_dx_add_entry() has 
to create a new index node and calls ext4_append(). In the end ext4_getblk() 
is called and it might get a buffer that has BH_Uptodate set, causing 
ext4_getblk() to not zero it out and leave the old content intact. 

I can reproduce this with plain linux-2.6.30.5. To produce this I use a nearly 
full filesystem and continuously create new files in one directory while 
removing other directories/files at the same time. 

Do I understand it correctly, that it happens when the newly allocated block 
(for the new index node) was very recently used by another file/directory, so 
that it is still in the buffer cache? But it surprises me that it doesn't 
happen more often.

Andreas Schlick