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Date: Thu, 27 Sep 2007 15:00:07 +0100
From: Christoph Hellwig <hch@infradead.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
       Trond Myklebust <Trond.Myklebust@netapp.com>,
       Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org, Christoph Hellwig <hch@infradead.org>
Subject: Re: lockdep wierdness...
Message-ID: <20070927140007.GA17543@infradead.org>
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	Peter Zijlstra <peterz@infradead.org>,
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On Thu, Sep 27, 2007 at 03:51:07PM +0200, Peter Zijlstra wrote:
> Christoph,
> 
> does Steve's story make sense? 

Yes.

> All that would need to be done is add an extra lock_class_key to
> file_system_type for i_mutex_dir_key, and extend alloc_inode to say
> something like:
> 
>   if (dir)
>     lockdep_set_class(&inode->i_mutex, &sb->s_type->i_mutex_dir_key);
>   else
>     lockdep_set_class(&inode->i_mutex, &sb->s_type->i_mutex_key);

Unfortunately we don't know what type of inode we have when calling
alloc_inode.  We only know it after reading in the inode from disk,
aka in unlock_new_inode.  Then again there is no reason to use
i_mutex before unlock_new_inode returns, so maybe we could defer
initializing it until unlock_new_inode.  I'm pretty sure we'll have
to fix a few filesystems that take i_mutex before that despite not
needing it, e.g. through i_size_write, though.