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Date: Wed, 26 Jul 2006 00:04:52 -0700
From: Andrew Morton <akpm@osdl.org>
To: Arjan van de Ven <arjan@linux.intel.com>
Cc: mingo@elte.hu, reiserfs-list@namesys.com, reiserfs-dev@namesys.com,
       viro@ftp.linux.org.uk, viro@zeniv.linux.org.uk, reiser@namesys.com,
       linux-kernel@vger.kernel.org, jesper.juhl@gmail.com
Subject: Re: [patch] lockdep: annotate vfs_rmdir for filesystems that take
 i_mutex in delete_inode
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On Wed, 26 Jul 2006 08:47:21 +0200
Arjan van de Ven <arjan@linux.intel.com> wrote:

> On Tue, 2006-07-25 at 22:33 -0700, Andrew Morton wrote:
> > On Wed, 26 Jul 2006 00:16:42 +0200
> > The VFS takes the directory i_mutex and reiserfs_delete_inode() takes the
> > to-be-deleted file's i_mutex.
> > 
> > That's notabug and lockdep will need to be taught about it.
> 
> [2nd try, now with coffee]
> 
> This is another 3 level locking ordering:
> do_rmdir takes the mutex of the parent directory
> vfs_rmdir takes the mutex of the victim
> shrink_dcache_parent ends up in the reiser delete_inode which takes the
> mutex of dead children of the victim
> 
> the I_MUTEX ordering rules are
> 
> I_MUTEX_PARENT -> I_MUTEX_CHILD -> <normal>
> 
> do_rmdir already has I_MUTEX_PARENT, delete_inode does <normal> so
> vfs_rmdir needs I_MUTEX_CHILD (which is also logical)
> 
> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
> 
> Index: linux-2.6.18-rc2-git5/fs/namei.c
> ===================================================================
> --- linux-2.6.18-rc2-git5.orig/fs/namei.c
> +++ linux-2.6.18-rc2-git5/fs/namei.c
> @@ -1967,7 +1967,7 @@ int vfs_rmdir(struct inode *dir, struct 
>  
>  	DQUOT_INIT(dir);
>  
> -	mutex_lock(&dentry->d_inode->i_mutex);
> +	mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD);
>  	dentry_unhash(dentry);
>  	if (d_mountpoint(dentry))
>  		error = -EBUSY;

If there's a reason why a filesystem shuld take an i_mutex under
vfs_rmdir() then fine.  But I don't think there is, in which case the
warning can be kept.

Can a reiserfs person please comment?