From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756419AbcBJBum (ORCPT ); Tue, 9 Feb 2016 20:50:42 -0500 Received: from ozlabs.org ([103.22.144.67]:50930 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755406AbcBJBul (ORCPT ); Tue, 9 Feb 2016 20:50:41 -0500 Message-ID: <1455069038.7576.6.camel@ellerman.id.au> Subject: Re: [PATCH v7 06/10] ppc64 ftrace: disable profiling for some functions From: Michael Ellerman To: Torsten Duwe Cc: Jiri Kosina , Miroslav Benes , Petr Mladek , Jessica Yu , Steven Rostedt , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Date: Wed, 10 Feb 2016 12:50:38 +1100 In-Reply-To: <20160204162107.65ECE692DF@newverein.lst.de> References: <20160204161527.5F3AC692CD@newverein.lst.de> <20160204162107.65ECE692DF@newverein.lst.de> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.5-1ubuntu3.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2016-01-25 at 16:31 +0100, Torsten Duwe wrote: > At least POWER7/8 have MMUs that don't completely autoload; > a normal, recoverable memory fault might pass through these functions. > If a dynamic tracer function causes such a fault, any of these functions > being traced with -mprofile-kernel may cause an endless recursion. I'm not really happy with this one, still :) At the moment I can trace these without any problems, with either ftrace or kprobes, but obviously it was causing you some trouble. So I'd like to understand why you were having issues when regular tracing doesn't. If it's the case that tracing can work for these functions, but live patching doesn't (for some reason), then maybe these should be blocked by the live patching infrastructure rather than at the ftrace/kprobes level. cheers