From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757045AbYEHA4b (ORCPT ); Wed, 7 May 2008 20:56:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751367AbYEHA4U (ORCPT ); Wed, 7 May 2008 20:56:20 -0400 Received: from relay2.sgi.com ([192.48.171.30]:55808 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750798AbYEHA4S (ORCPT ); Wed, 7 May 2008 20:56:18 -0400 Date: Wed, 7 May 2008 17:56:17 -0700 (PDT) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Linus Torvalds cc: Andrew Morton , Andrea Arcangeli , steiner@sgi.com, holt@sgi.com, npiggin@suse.de, a.p.zijlstra@chello.nl, kvm-devel@lists.sourceforge.net, kanojsarcar@yahoo.com, rdreier@cisco.com, swise@opengridcomputing.com, linux-kernel@vger.kernel.org, avi@qumranet.com, linux-mm@kvack.org, general@lists.openfabrics.org, hugh@veritas.com, rusty@rustcorp.com.au, aliguori@us.ibm.com, chrisw@redhat.com, marcelo@kvack.org, dada1@cosmosbay.com, paulmck@us.ibm.com Subject: Re: [PATCH 08 of 11] anon-vma-rwsem In-Reply-To: Message-ID: References: <6b384bb988786aa78ef0.1210170958@duo.random> <20080507212650.GA8276@duo.random> <20080507222205.GC8276@duo.random> <20080507153103.237ea5b6.akpm@linux-foundation.org> <20080507224406.GI8276@duo.random> <20080507155914.d7790069.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 7 May 2008, Linus Torvalds wrote: > On Wed, 7 May 2008, Christoph Lameter wrote: > > > > Multiple vmas may share the same mapping or refer to the same anonymous > > vma. The above code will deadlock since we may take some locks multiple > > times. > > Ok, so that actually _is_ a problem. It would be easy enough to also add > just a flag to the vma (VM_MULTILOCKED), which is still cleaner than doing > a vmalloc and a whole sort thing, but if this is really rare, maybe Ben's > suggestion of just using stop-machine is actually the right one just > because it's _so_ simple. Set the vma flag when we locked it and then skip when we find it locked right? This would be in addition to the global lock? stop-machine would work for KVM since its a once in a Guest OS time of thing. But GRU, KVM and eventually Infiniband need the ability to attach in a reasonable timeframe without causing major hiccups for other processes. > (That said, we're not running out of vm flags yet, and if we were, we > could just add another word. We're already wasting that space right now on > 64-bit by calling it "unsigned long"). We sure have enough flags.