From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [EXT4 set 4][PATCH 1/5] i_version:64 bit inode version
Date: Tue, 10 Jul 2007 22:22:09 -0700
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Cc: linux-fsdevel@vger.kernel.org, nfsv4@linux-nfs.org,
	linux-ext4@vger.kernel.org, cmm@us.ibm.com, linux-kernel@vger.kernel.org
To: Neil Brown <neilb@suse.de>
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On Wed, 11 Jul 2007 15:05:27 +1000 Neil Brown <neilb@suse.de> wrote:

> 
> It just occurred to me:
> 
>  If i_version is 64bit, then knfsd would need to be careful when
>  reading it on a 32bit host.  What are the locking rules?
> 
>  Presumably it is only updated under i_mutex protection, but having to
>  get i_mutex to read it would seem a little heavy handed.
> 
>  Should it use a seqlock like i_size?
>  Could we use the same seqlock that i_size uses, or would we need a
>  separate one?
> 

seqlocks are a bit of a pain to use (we've had plenty of deadlocks on the
i_size one).  We could reuse inode.i_lock for this modification.  Its
mandate is "general purpose innermost lock to protect stuff in this inode".