linux-kernel - Re: [PATCH][BUGFIX] configfs: Fix symlink() to a removing item

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Message-ID: <20080617104259.GX30804@localhost>
Date:	Tue, 17 Jun 2008 12:42:59 +0200
From:	Louis Rilling <Louis.Rilling@...labs.com>
To:	Joel.Becker@...cle.com
Cc:	linux-kernel@...r.kernel.org, ocfs2-devel@....oracle.com
Subject: Re: [PATCH][BUGFIX] configfs: Fix symlink() to a removing item

On Mon, Jun 16, 2008 at 03:29:00PM -0700, Joel Becker wrote:
> On Mon, Jun 16, 2008 at 08:09:11PM +0200, Louis Rilling wrote:
> > This patch introduces a similar (weird?) behavior as with mkdir failures making
> > rmdir fail: if symlink() races with rmdir() of the parent directory (or its
> > youngest user-created ancestor if parent is a default group) or rmdir() of the
> > target directory, and then fails in configfs_create(), this can make the racing
> > rmdir() fail despite the concerned directory having no user-created entry (resp.
> > no symlink pointing to it or one of its default groups) in the end.
> > If this behavior is found unacceptable, I'll submit a fix in the same spirit as
> > the racing mkdir() fix.
> 
> 	Ahh, but you can't wait on the mutex like you do in mkdir(),
> because they're not ordered - it can race rename again.

Yes I can. In the mkdir() case, rmdir() waits on the mutex of one of the default
groups. The symlink case will be handled the same. The difference is that while
mkdir() tags the parent with CONFIGFS_USET_IN_MKDIR, symlink() will tag both the
parent and the target with CONFIGFS_USET_IN_SYMLINK. [ We can actually merge the
two flags in something like CONFIGFS_USET_ATTACHING. ] Since tagging requires
only to take configfs_dirent_lock, there will be no deadlock.

I'll send a patch later.

Louis

-- 
Dr Louis Rilling			Kerlabs
Skype: louis.rilling			Batiment Germanium
Phone: (+33|0) 6 80 89 08 23		80 avenue des Buttes de Coesmes
http://www.kerlabs.com/			35700 Rennes

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