Date: Tue, 17 Jun 2008 14:56:50 +0200
From: Louis Rilling <Louis.Rilling@kerlabs.com>
To: Joel.Becker@oracle.com
Cc: linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com
Subject: Re: [PATCH][BUGFIX] configfs: Fix symlink() to a removing item
Message-ID: <20080617125650.GY30804@localhost>
Reply-To: Louis.Rilling@kerlabs.com
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On Tue, Jun 17, 2008 at 12:42:59PM +0200, Louis Rilling wrote:
> 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 failu=
res 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 e=
ntry (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.
> >=20
> > 	Ahh, but you can't wait on the mutex like you do in mkdir(),
> > because they're not ordered - it can race rename again.
>=20
> 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 b=
oth the
> parent and the target with CONFIGFS_USET_IN_SYMLINK. [ We can actually me=
rge the
> two flags in something like CONFIGFS_USET_ATTACHING. ] Since tagging requ=
ires
> only to take configfs_dirent_lock, there will be no deadlock.

Hm, you were right, sorry. We can only solve the race with rmdir() removing=
 the
item where the symlink is created. For the target item, I don't know yet...

Louis

--=20
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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