From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753257AbXGLEZu (ORCPT ); Thu, 12 Jul 2007 00:25:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751231AbXGLEZk (ORCPT ); Thu, 12 Jul 2007 00:25:40 -0400 Received: from smtp2.linux-foundation.org ([207.189.120.14]:54893 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751245AbXGLEZk (ORCPT ); Thu, 12 Jul 2007 00:25:40 -0400 Date: Wed, 11 Jul 2007 21:24:35 -0700 From: Andrew Morton To: Rusty Russell Cc: David Miller , hch@lst.de, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: lguest, Re: -mm merge plans for 2.6.23 Message-Id: <20070711212435.abd33524.akpm@linux-foundation.org> In-Reply-To: <1184208521.6005.695.camel@localhost.localdomain> References: <20070710013152.ef2cd200.akpm@linux-foundation.org> <20070711122324.GA21714@lst.de> <1184203311.6005.664.camel@localhost.localdomain> <20070711.192829.08323972.davem@davemloft.net> <1184208521.6005.695.camel@localhost.localdomain> X-Mailer: Sylpheed 2.4.1 (GTK+ 2.8.17; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 12 Jul 2007 12:48:41 +1000 Rusty Russell wrote: > On Wed, 2007-07-11 at 19:28 -0700, David Miller wrote: > > From: Rusty Russell > > Date: Thu, 12 Jul 2007 11:21:51 +1000 > > > > > To do inter-guest (ie. inter-process) I/O you really have to make sure > > > the other side doesn't go away. > > > > You should just let it exit and when it does you receive some kind of > > exit notification that resets your virtual device channel. > > > > I think the reference counting approach is error and deadlock prone. > > Be more loose and let the events reset the virtual devices when > > guests go splat. > > There are two places where we grab task refcnt. One might be avoidable > (will test and get back) but the deferred wakeup isn't really: > > /* We cache one process to wakeup: helps for batching & wakes outside locks. */ > void set_wakeup_process(struct lguest *lg, struct task_struct *p) > { > if (p == lg->wake) > return; > > if (lg->wake) { > wake_up_process(lg->wake); > put_task_struct(lg->wake); > } > lg->wake = p; > if (lg->wake) > get_task_struct(lg->wake); > } We seem to be taking the reference against the wrong thing here. It should be against the mm, not against a task_struct? From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 11 Jul 2007 21:24:35 -0700 From: Andrew Morton Subject: Re: lguest, Re: -mm merge plans for 2.6.23 Message-Id: <20070711212435.abd33524.akpm@linux-foundation.org> In-Reply-To: <1184208521.6005.695.camel@localhost.localdomain> References: <20070710013152.ef2cd200.akpm@linux-foundation.org> <20070711122324.GA21714@lst.de> <1184203311.6005.664.camel@localhost.localdomain> <20070711.192829.08323972.davem@davemloft.net> <1184208521.6005.695.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Rusty Russell Cc: David Miller , hch@lst.de, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Thu, 12 Jul 2007 12:48:41 +1000 Rusty Russell wrote: > On Wed, 2007-07-11 at 19:28 -0700, David Miller wrote: > > From: Rusty Russell > > Date: Thu, 12 Jul 2007 11:21:51 +1000 > > > > > To do inter-guest (ie. inter-process) I/O you really have to make sure > > > the other side doesn't go away. > > > > You should just let it exit and when it does you receive some kind of > > exit notification that resets your virtual device channel. > > > > I think the reference counting approach is error and deadlock prone. > > Be more loose and let the events reset the virtual devices when > > guests go splat. > > There are two places where we grab task refcnt. One might be avoidable > (will test and get back) but the deferred wakeup isn't really: > > /* We cache one process to wakeup: helps for batching & wakes outside locks. */ > void set_wakeup_process(struct lguest *lg, struct task_struct *p) > { > if (p == lg->wake) > return; > > if (lg->wake) { > wake_up_process(lg->wake); > put_task_struct(lg->wake); > } > lg->wake = p; > if (lg->wake) > get_task_struct(lg->wake); > } We seem to be taking the reference against the wrong thing here. It should be against the mm, not against a task_struct? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org