Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762157AbdDSKNn (ORCPT ); Wed, 19 Apr 2017 06:13:43 -0400 Received: from ozlabs.org ([103.22.144.67]:51879 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761917AbdDSKNl (ORCPT ); Wed, 19 Apr 2017 06:13:41 -0400 From: Michael Ellerman To: "Oliver O'Halloran" , Rob Herring Cc: "devicetree\@vger.kernel.org" , linuxppc-dev , "linux-kernel\@vger.kernel.org" , rostedt@goodmis.org, Ingo Molnar , Tyrel Datwyler , Nathan Fontenot , Frank Rowand Subject: Re: [PATCH] of: introduce event tracepoints for dynamic device_node lifecyle In-Reply-To: References: <1492475525-10827-1-git-send-email-tyreld@linux.vnet.ibm.com> User-Agent: Notmuch/0.21 (https://notmuchmail.org) Date: Wed, 19 Apr 2017 20:13:38 +1000 Message-ID: <87y3uw66y5.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1542 Lines: 31 Oliver O'Halloran writes: > On Wed, Apr 19, 2017 at 2:46 AM, Rob Herring wrote: >> On Mon, Apr 17, 2017 at 7:32 PM, Tyrel Datwyler >> wrote: >>> This patch introduces event tracepoints for tracking a device_nodes >>> reference cycle as well as reconfig notifications generated in response >>> to node/property manipulations. >>> >>> With the recent upstreaming of the refcount API several device_node >>> underflows and leaks have come to my attention in the pseries (DLPAR) dynamic >>> logical partitioning code (ie. POWER speak for hotplugging virtual and physcial >>> resources at runtime such as cpus or IOAs). These tracepoints provide a >>> easy and quick mechanism for validating the reference counting of >>> device_nodes during their lifetime. >> >> Not really relevant for this patch, but since you are looking at >> pseries and refcounting, the refcounting largely exists for pseries. >> It's also hard to get right as this type of fix is fairly common. It's >> now used for overlays, but we really probably only need to refcount >> the overlays or changesets as a whole, not at a node level. If you >> have any thoughts on how a different model of refcounting could work >> for pseries, I'd like to discuss it. > > One idea I've been kicking around is differentiating short and long > term references to a node. I actually did this a long time ago, but balked at the size of the patch to do the conversion. Let me see if I can find it lying around ... cheers