linux-ext4 - Re: [PATCH] ext4: add checksum calculation when clearing UNINIT flag

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Message-ID: <20081107143806.GD9543@mit.edu>
Date:	Fri, 7 Nov 2008 09:38:06 -0500
From:	Theodore Tso <tytso@....edu>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Frédéric Bohé <frederic.bohe@...l.net>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: add checksum calculation when clearing UNINIT
	flag

On Fri, Nov 07, 2008 at 07:57:18PM +0530, Aneesh Kumar K.V wrote:
> On Fri, Nov 07, 2008 at 08:52:22AM -0500, Theodore Tso wrote:
> > On Fri, Nov 07, 2008 at 11:22:56AM +0100, Frédéric Bohé wrote:
> > > From: Frederic Bohe <frederic.bohe@...l.net>
> > > 
> > > Block group's checksum need to be re-calculated during the
> > > initialization of an UNINIT'd group. This fix a race when several
> > > threads try to allocate a new inode in an UNINIT'd group.
> > 
> > This patch looks sane, and so I'll accept it, but there's a higher
> > order hiding here ---- why are we initializing the block bitmap in
> > ext4_new_inode()?  Sure, *most* of the time where we create a new
> > inode, we'll be needing to allocate a new block, but sometimes we
> > won't (i.e., when creating a symlink, device file, socket, or a
> > zero-length regular file).  
> 
> Because when we clear the uninitt_bg flag the kernel expect the block 
> bitmap to be correctly indicate blocks containing block
> bitmap and inode bitmap as used. If mke2fs didn't do that we would
> need to do the same when we remove the uninit_bg flag.

We have separate flags inidicating whether the block allocation bitmap
and inode allocation bitmaps are initialized or not,
EXT4_BG_BLOCK_UNINIT, and EXT4_BG_INODE_UNINIT, respectively.  So what
I am proposing is to not initialize the block bitmap in
ext4_new_inode(), and not to clear the EXT4_BG_BLOCK_UNINIT flag, either.

		  		      	     	       - Ted
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