From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jamie Lokier Subject: Re: [PATCH] fix race in mark_mounts_for_expiry() Date: Wed, 18 May 2005 13:50:41 +0100 Message-ID: <20050518125041.GA29107@mail.shareable.org> References: <1116360352.24560.85.camel@localhost> <1116399887.24560.116.camel@localhost> <1116400118.24560.119.camel@localhost> <6865.1116412354@redhat.com> <7230.1116413175@redhat.com> <1116414429.10773.57.camel@lade.trondhjem.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: trond.myklebust@fys.uio.no, dhowells@redhat.com, linuxram@us.ibm.com, viro@parcelfarce.linux.theplanet.co.uk, akpm@osdl.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Return-path: Received: from mail.shareable.org ([81.29.64.88]:27352 "EHLO mail.shareable.org") by vger.kernel.org with ESMTP id S261509AbVERMvK (ORCPT ); Wed, 18 May 2005 08:51:10 -0400 To: Miklos Szeredi Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Miklos Szeredi wrote: > > Some archs already have an atomic_dec_if_positive() (see for instance > > the PPC). It won't take much work to convert that to an > > atomic_inc_if_positive(). > > > > For those arches that don't have that sort of thing, then writing a > > generic atomic_inc_if_positive() using cmpxchg() will often be possible, > > but there are exceptions (for instance the original 386 does not have a > > cmpxchg, so there you will have to use something else). > > The problem with introducing architecture specific code, is that it's > just asking for new bugs. > > If it's something used all over the kernel, than obviously it's OK, > but for the sake of just one caller it's a bit crazy I think. I agree. And I think you're just adding to the case for removing mnt_namespace entirely. We'd still keep CLONE_NS, and users currently using namespaces (in the normal ways) would see no difference. mnt_namespace has these visible effects: - Prevents some tasks from mounting/umounting in a "foreign" namespace, even when they are granted access to the directory tree of the foreign namespace. It's not clear if the restriction is a useful security tool. - Causes every mount in a mount tree to be detached (independently), when last task associated with a namespace is destroyed. And this invisible effect: - More concurrency than a global mount lock would have. Is that all? Are any of these effects important enough to keep? -- Jamie