From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757693AbZF2JmZ (ORCPT ); Mon, 29 Jun 2009 05:42:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753061AbZF2JmR (ORCPT ); Mon, 29 Jun 2009 05:42:17 -0400 Received: from mx2.redhat.com ([66.187.237.31]:38821 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751611AbZF2JmQ (ORCPT ); Mon, 29 Jun 2009 05:42:16 -0400 Date: Mon, 29 Jun 2009 12:41:46 +0300 From: "Michael S. Tsirkin" To: Avi Kivity Cc: Gregory Haskins , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mtosatti@redhat.com, paulmck@linux.vnet.ibm.com, markmc@redhat.com Subject: Re: [PATCHv2] kvm: remove in_range and switch to rwsem for iobus Message-ID: <20090629094146.GC19167@redhat.com> References: <20090628193425.GA14204@redhat.com> <4A487D2C.2020007@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A487D2C.2020007@redhat.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 29, 2009 at 11:37:00AM +0300, Avi Kivity wrote: > On 06/28/2009 10:34 PM, Michael S. Tsirkin wrote: >> This changes bus accesses to use high-level kvm_io_bus_read/kvm_io_bus_write >> functions, which utilize read/write semaphore intead of mutex. in_range now >> becomes unused so it is removed from device ops in favor of read/write >> callbacks performing range checks internally. >> >> This allows aliasing (mostly for in-kernel virtio), as well as better error >> handling by making it possible to pass errors up to userspace. And it's enough >> to look at the diffstat to see that it's a better API anyway. >> >> While we are at it, document locking rules for kvm_io_device_ops. >> >> Note: since the use of the new bus_lock is localized to a small number of >> places, it will be easy to switch to srcu in the future if we so desire. >> > > Looks good. But please split into a locking change patch and an API > change patch (in whatever order makes more sense). This is harder than it seems. Is this really important? The locking change itself is about 6 lines, but 1. if I do it after in_range removal I get deadlocks as after marcelo's change kvm->lock is taken internally by writers. 2. if I do it before in_range removal it's a lot of churn: one of the reasons for code reorg is so that there are less places to change locking. > I think you can reuse slots_lock instead of adding a new lock. IIRC > slots_lock is already taken for read everywhere, so you only need to > take it for write when registering things. > > -- > error compiling committee.c: too many arguments to function