linux-kernel - Re: NFS lockdep lock misordering mmap_sem<->i_mutex

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Date:	Mon, 7 Dec 2009 14:20:09 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Trond.Myklebust@...app.com
Subject: Re: NFS lockdep lock misordering mmap_sem<->i_mutex_key with 2.6.32-git1

On Mon, Dec 07, 2009 at 09:19:28PM +0900, KOSAKI Motohiro wrote:
> > 
> > While booting 2.6.32-git1 on a NFS root box I got the following
> > lockdep warning early at boot. I haven't looked at details.
> 
> It seems typical ABBA deadlock.
> 
>  vfs_readdir				[grab i_mutex]
>    nfs_readdir
>      nfs_do_filldir
>        filldir
>          copy_to_user
>            [page_fault]			[grab mmap_sem]
> 
>  sys_mmap				[grab mmap_sem]
>    do_mmap_pgoff
>      mmap_region
>        nfs_file_mmap
>          nfs_revalidate_mapping  
>            nfs_invalidate_mapping	[grab i_mutex]
> 
> I guess recent lockdep improvement find old bug.

Thanks for the analysis.

I guess should never do copy_*_user while holding i_mutex? There might
be lots of cases like that.

-Andi
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