linux-kernel - Re: lockdep wierdness...

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Message-ID: <20070927140007.GA17543@infradead.org>
Date:	Thu, 27 Sep 2007 15:00:07 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: lockdep wierdness...

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.
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