linux-ext4 - Re: i_mutex questions

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Date:	Tue, 13 Sep 2011 12:02:09 -0700
From:	Joel Becker <jlbec@...lplan.org>
To:	Allison Henderson <achender@...ux.vnet.ibm.com>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Ted Ts'o <tytso@....edu>
Subject: Re: i_mutex questions

On Tue, Sep 13, 2011 at 11:33:29AM -0700, Allison Henderson wrote:
> Hi All,
> 
> I have been trying to find a way to synchronize punch hole with read
> and write operations with out the use of i_mutex.  The concern is
> that after punch hole has released the pages inside the hole,
> another process may remap the page to a block before punch has taken
> i_data_sem.  I think putting i_mutex around the punch hole operation
> would fix this, but since we are trying to avoid further improper
> use of i_mutex, I am trying to avoid that solution.

Hey Allison,
	Actually, i_mutex is the normal way to handle this.  ocfs2 takes
i_mutex down under its ->fallocate().  Truncate is in the same boat,
which is why do_truncate() takes i_mutex before calling notify_change().
	The read-write paths grab i_mutex for buffered operation.  They
don't for O_DIRECT, which doesn't map to the pagecache.  This is where
i_data_sem should speed things up.  

Joel


-- 

"Anything that is too stupid to be spoken is sung."  
        - Voltaire

			http://www.jlbec.org/
			jlbec@...lplan.org
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