linux-kernel - Re: [BUGFIX][PATCH 3/3] configfs: Fix failing symlink() making rmdir() fail

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Date:	Wed, 18 Jun 2008 13:11:07 -0700
From:	Joel Becker <Joel.Becker@...cle.com>
To:	Louis Rilling <Louis.Rilling@...labs.com>
Cc:	linux-kernel@...r.kernel.org, ocfs2-devel@....oracle.com
Subject: Re: [BUGFIX][PATCH 3/3] configfs: Fix failing symlink() making
	rmdir() fail

On Wed, Jun 18, 2008 at 01:40:43PM +0200, Louis Rilling wrote:
> The problem is rmdir() of the target item (see below). ATTACHING only protects
> us from rmdir() of the parent. This is the exact reason why I attach the link to
> the target in last place, where we know that we won't have to rollback.

	Why wouldn't it protect the target, given that detach_prep()
will be called against the target if it's being rmdir'd?

> 	And AFAICS, creating a VFS object can not hurt as long as we hold the
> parent i_mutex, right? Otherwise there already is a problem in
> configfs_attach_item() where a failure in populate_attrs() leads to rollback the
> creation of the VFS object already created for the item.

	We *can* do that, but we try to isolate it - hand-building VFS
objects is complex and error prone, and I try to isolate that to
specific cases.  I'd rather avoid it when not necessary.

> > 		spin_lock(&configfs_dirent_lock);
> > 		parent_sd->s_type &= ~CONFIGFS_USET_ATTACHING;
> > 		if (ret) {
> 
> Here, if detach_prep() of the target failed because of the link attached above,
> it had no means to retry. rmdir() of the target fails because of this
> temporary link, which results in a failing symlink() making rmdir() of the
> target fail.

	How so?  It sees ATTACHING, it gets -EAGAIN, it tries again,
just like before.  What's different?

Joel

-- 

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

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@...cle.com
Phone: (650) 506-8127
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