From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754498AbaCKC6Y (ORCPT ); Mon, 10 Mar 2014 22:58:24 -0400 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.232]:19278 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754422AbaCKC6W (ORCPT ); Mon, 10 Mar 2014 22:58:22 -0400 Date: Mon, 10 Mar 2014 22:58:20 -0400 From: Steven Rostedt To: fche@redhat.com (Frank Ch. Eigler) Cc: Mathieu Desnoyers , linux-kernel@vger.kernel.org, Ingo Molnar , Frederic Weisbecker , Andrew Morton , Johannes Berg Subject: Re: [for-next][PATCH 08/20] tracing: Warn if a tracepoint is not set via debugfs Message-ID: <20140310225820.0f02025d@gandalf.local.home> In-Reply-To: References: <20140307150920.881849073@goodmis.org> <20140307151202.210588176@goodmis.org> <241011797.35066.1394481694124.JavaMail.zimbra@efficios.com> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.130:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 10 Mar 2014 22:41:31 -0400 fche@redhat.com (Frank Ch. Eigler) wrote: > > Hi - > > > >> From: Steven Rostedt > >> > >> Tracepoints were made to allow enabling a tracepoint in a module before that > >> module was loaded. When a tracepoint is enabled and it does not exist, the > >> name is stored and will be enabled when the tracepoint is created. > >> > >> The problem with this approach is that when a tracepoint is enabled when > >> it expects to be there, it gives no warning that it does not exist. > > So it is a deferred-activation kind of call, with no way of knowing > when or if the tracepoints will start coming in. Why is that > supported at all, considering that clients could monitor modules > coming & going via the module_notifier chain, and update registration > at that time? That's my argument. > > > >> + entry = get_tracepoint(name); > >> + /* Make sure the entry was enabled */ > >> + if (!entry || !entry->enabled) > >> + ret = -ENODEV; > > For what it's worth, I agree with Mathieu that this sort of successful > failure result code is a problem for tracking what needs cleanup and > what doesn't. (In systemtap's case, if this change gets merged, we'll > have to treat -ENODEV as if it were 0.) Does systemtap enable tracepoints before they are created? That is, do you allow enabling of a tracepoint in a module that is not loaded yet? If not, than you want this as an error. -- Steve