From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759256AbdDSCbu (ORCPT ); Tue, 18 Apr 2017 22:31:50 -0400 Received: from mail-pf0-f196.google.com ([209.85.192.196]:35213 "EHLO mail-pf0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759240AbdDSCbr (ORCPT ); Tue, 18 Apr 2017 22:31:47 -0400 Subject: Re: [PATCH] of: introduce event tracepoints for dynamic device_node lifecyle To: Michael Ellerman , Tyrel Datwyler , robh+dt@kernel.org References: <1492475525-10827-1-git-send-email-tyreld@linux.vnet.ibm.com> <58F6AA35.2040902@gmail.com> <87efwp6v4e.fsf@concordia.ellerman.id.au> Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, nfont@linux.vnet.ibm.com, rostedt@goodmis.org, mingo@redhat.com From: Frank Rowand Message-ID: <58F6CBF9.7060000@gmail.com> Date: Tue, 18 Apr 2017 19:31:21 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 MIME-Version: 1.0 In-Reply-To: <87efwp6v4e.fsf@concordia.ellerman.id.au> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/18/17 18:31, Michael Ellerman wrote: > Frank Rowand writes: > >> On 04/17/17 17:32, 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. >>> >>> Further, when pseries lpars are migrated to a different machine we >>> perform a live update of our device tree to bring it into alignment with the >>> configuration of the new machine. The of_reconfig_notify trace point >>> provides a mechanism that can be turned for debuging the device tree >>> modifications with out having to build a custom kernel to get at the >>> DEBUG code introduced by commit 00aa3720. >> >> I do not like changing individual (or small groups of) printk() style >> debugging information to tracepoint style. > > I'm not quite sure which printks() you're referring to. > > The only printks that are removed in this series are under #ifdef DEBUG, > and so are essentially not there unless you build a custom kernel. Yes, I am talking about pr_debug(), pr_info(), pr_err(), etc. > > They also only cover the reconfig case, which is actually less > interesting than the much more common and bug-prone get/put logic. When I was looking at the get/put issue I used pr_debug(). >> As far as I know, there is no easy way to combine trace data and printk() >> style data to create a single chronology of events. If some of the >> information needed to debug an issue is trace data and some is printk() >> style data then it becomes more difficult to understand the overall >> situation. > > If you enable CONFIG_PRINTK_TIME then you should be able to just sort > the trace and the printk output by the timestamp. If you're really > trying to correlate the two then you should probably just be using > trace_printk(). Except the existing debug code that uses pr_debug() does not use trace_printk(). And "just sort" does not apply to multi-line output like: cpuhp/23-147 [023] .... 128.324827: of_node_put: refcount=5, dn->full_name=/cpus/PowerPC,POWER8@10 cpuhp/23-147 [023] .... 128.324829: of_node_put: refcount=4, dn->full_name=/cpus/PowerPC,POWER8@10 cpuhp/23-147 [023] .... 128.324829: of_node_put: refcount=3, dn->full_name=/cpus/PowerPC,POWER8@10 cpuhp/23-147 [023] .... 128.324831: of_node_put: refcount=2, dn->full_name=/cpus/PowerPC,POWER8@10 drmgr-7284 [009] .... 128.439000: of_node_put: refcount=1, dn->full_name=/cpus/PowerPC,POWER8@10 drmgr-7284 [009] .... 128.439002: of_reconfig_notify: action=DETACH_NODE, dn->full_name=/cpus/PowerPC,POWER8@10, prop->name=null, old_prop->name=null drmgr-7284 [009] .... 128.439015: of_node_put: refcount=0, dn->full_name=/cpus/PowerPC,POWER8@10 drmgr-7284 [009] .... 128.439016: of_node_release: dn->full_name=/cpus/PowerPC,POWER8@10, dn->_flags=4 I was kinda hoping that maybe someone had already created a tool to deal with this issue. But not too optimistic. > But IMO this level of detail, tracing every get/put, does not belong in > printk. Trace points are absolutely the right solution for this type of > debugging. > > cheers > . >