linux-ext4 - lock i_mutex for fallocate?

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Date:	Wed, 31 Aug 2011 17:33:25 -0700
From:	Allison Henderson <achender@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
CC:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Andreas Dilger <adilger@...ger.ca>
Subject: lock i_mutex for fallocate?

Hi All,

In ext4 punch hole, we realized that the punch hole operation needs to 
be done under i_mutex just like truncate.  i_mutex for truncate is held 
in the vfs layer, so we dont need to lock it at the file system layer, 
but vfs does not lock i_mutex for fallocate.  We can lock i_mutex for 
fallocate at the fs layer, but question was raised then: should i_mutex 
for fallocate be held in the vfs layer instead?  I do not know if other 
file systems need i_mutex to be locked for fallocate, or if they might 
be locking it already, so I am doing some investigating on this idea, 
and also the appropriate use of i_mutex in general.  Can someone provide 
some insight this topic?  Thx!

Allison Henderson
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