linux-kernel - Re: [PATCH] hugetlbfs: lockdep annotate root inode properly

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Date:	Thu, 8 Mar 2012 14:45:26 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Tyler Hicks <tyhicks@...onical.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	linux-mm@...ck.org, jboyer@...hat.com,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH] hugetlbfs: lockdep annotate root inode properly

On Thu, 8 Mar 2012 17:33:34 -0500
Dave Jones <davej@...hat.com> wrote:

> On Thu, Mar 08, 2012 at 02:19:38PM -0800, Andrew Morton wrote:
>  > On Thu, 8 Mar 2012 21:49:52 +0000
>  > Al Viro <viro@...IV.linux.org.uk> wrote:
>  > 
>  > > > So we need to pull the i_mutex out of hugetlbfs_file_mmap().
>  > > 
>  > > IIRC, you have a patch in your tree doing just that...
>  > 
>  > Nope.
>  > 
>  > But it seems that you've recently seen such a patch - can you recall
>  > where?
> 
> this ? https://lkml.org/lkml/2012/2/23/64
> 

Thanks, yes, probably that.  Needs the i_size_read()/write() changes.

I worry a bit about the region handling code in mm/hugetlb.c.  

 * The region data structures are protected by a combination of the mmap_sem
 * and the hugetlb_instantion_mutex.  To access or modify a region the caller
 * must either hold the mmap_sem for write, or the mmap_sem for read and
 * the hugetlb_instantiation mutex:

I hope that's true - it would be nice to have some debug assertions in
the various region_foo() functions to verify that the required locks are
held.

But if that code is all nice and tight, I guess that removing that
i_mutex acquisition will be pretty simple.

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