Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754227Ab2HOMfZ (ORCPT ); Wed, 15 Aug 2012 08:35:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51935 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751691Ab2HOMfY (ORCPT ); Wed, 15 Aug 2012 08:35:24 -0400 Date: Wed, 15 Aug 2012 09:34:58 -0300 From: Rafael Aquini To: "Michael S. Tsirkin" Cc: Rusty Russell , linux-mm@kvack.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Rik van Riel , Mel Gorman , Andi Kleen , Andrew Morton , Konrad Rzeszutek Wilk , Minchan Kim Subject: Re: [PATCH v7 2/4] virtio_balloon: introduce migration primitives to balloon pages Message-ID: <20120815123457.GA2175@t510.redhat.com> References: <20120813084123.GF14081@redhat.com> <87lihis5qi.fsf@rustcorp.com.au> <20120814083320.GA3597@redhat.com> <20120814184409.GC13338@t510.redhat.com> <20120814193109.GA28840@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120814193109.GA28840@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1139 Lines: 27 On Tue, Aug 14, 2012 at 10:31:09PM +0300, Michael S. Tsirkin wrote: > > > now CPU1 executes the next instruction: > > > > > > } > > > > > > which would normally return to function's caller, > > > but it has been overwritten by CPU2 so we get corruption. > > > > > > No? > > > > At the point CPU2 is unloading the module, it will be kept looping at the > > snippet Rusty pointed out because the isolation / migration steps do not mess > > with 'vb->num_pages'. The driver will only unload after leaking the total amount > > of balloon's inflated pages, which means (for this hypothetical case) CPU2 will > > wait until CPU1 finishes the putaback procedure. > > > > Yes but only until unlock finishes. The last return from function > is not guarded and can be overwritten. CPU1 will be returning to putback_balloon_page() which code is located at core mm/compaction.c, outside the driver. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/