Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752852AbbHZU4V (ORCPT ); Wed, 26 Aug 2015 16:56:21 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:41197 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752525AbbHZU4S (ORCPT ); Wed, 26 Aug 2015 16:56:18 -0400 Date: Wed, 26 Aug 2015 13:56:16 -0700 From: Andrew Morton To: Vince Weaver Cc: Peter Zijlstra , Ingo Molnar , Johannes Berg , Linus Torvalds , Thomas Gleixner , adrian.hunter@intel.com, Ingo Molnar , Borislav Petkov , Arnaldo Carvalho de Melo , linux-kernel@vger.kernel.org, Alexander Shishkin , "H. Peter Anvin" , Stephane Eranian Subject: Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Message-Id: <20150826135616.c96aeed77efbb412d72b8f00@linux-foundation.org> In-Reply-To: References: <20150825091740.GA23488@gmail.com> <1440495246.2192.13.camel@sipsolutions.net> <20150825100728.GA1820@gmail.com> <1440497981.2192.39.camel@sipsolutions.net> <20150826044948.GC14584@gmail.com> <1440572775.1932.1.camel@sipsolutions.net> <20150826072020.GA19081@gmail.com> <20150826072656.GA19305@gmail.com> <20150826114111.01675d8eadda78d82933d8a5@linux-foundation.org> <20150826200513.GX16853@twins.programming.kicks-ass.net> <20150826132249.fbb2aa602525c7df4a1f86ed@linux-foundation.org> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2639 Lines: 60 On Wed, 26 Aug 2015 16:50:33 -0400 (EDT) Vince Weaver wrote: > On Wed, 26 Aug 2015, Andrew Morton wrote: > > > On Wed, 26 Aug 2015 22:05:13 +0200 Peter Zijlstra wrote: > > > > > > Is this whole thing overkill? As far as I can see, the problem which is > > > > being addressed only occurs in a couple of places (perf, wifi netlink > > > > handling) and could be addressed with some local pr_debug statements. ie, > > > > > > > > #define err_str(e, s) ({ > > > > if (debugging) > > > > pr_debug("%s:%d: error %d (%s)", __FILE__, __LINE__, e, s); > > > > e; > > > > }) > > > > > > > > (And I suppose that if this is later deemed inadequate, err_str() could > > > > be made more fancy). > > > > > > Not really. That is something that's limited to root. Whereas the > > > problem is very much wider than that. > > > > > > If you set one bit wrong in the pretty large perf_event_attr you've got > > > a fair chance of getting -EINVAL on trying to create the event. Good > > > luck finding what you did wrong. > > > > > > Any user can create events (for their own tasks), this does not require > > > root. > > > > > > Allowing users to flip your @debugging flag would be an insta DoS. > > > > > > Furthermore, its very unfriendly in that you have to (manually) go > > > correlate random dmesg output with some program action. > > > > It depends on who the audience is. If it's developers who are writing > > userspace perf tooling then all the above won't be an issue. If it's > > aimed at end users of that tooling then yes. > > As a developer of tools that use the perf_event interface directly (PAPI > and such) I can say this is a common problem (getting unexplained EINVAL > results) and yes, telling the user to recompile their kernel to enable > debugging is usually not an option. Users wouldn't need to recompile. > I often have to resort to sprinkling the kernel with printks to find the > source of errors, which is a pain. It's even more fun when the user's > setup is slightly different enough that I can't reproduce the issue on a > local machine, which happens often (due to different kernels, distros > backporting perf fixes, different hardware, different security settings, > etc). Suppose you were to tell them "please do `echo 1 > /proc/whatever' then send me the kernel logs". Would this be good enough? -- 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/