From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934708AbcA1IJM (ORCPT ); Thu, 28 Jan 2016 03:09:12 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:39944 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934490AbcA1IJK (ORCPT ); Thu, 28 Jan 2016 03:09:10 -0500 Date: Thu, 28 Jan 2016 09:08:59 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, Paul McKenney , Mathieu Desnoyers Subject: [RFC][BUG] tracer: Fails to work Message-ID: <20160128080859.GB6357@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steve, So I was hunting wabbits the other day and ftrace failed to work. After I cursed a bit on IRC, Thomas found the below, after 'fixing' it like so things worked enough to get the trace out. Relying on things like this make it entirely impossible to get any trace data out if you've wedged a CPU. Exactly the kind of situation you want trace data for. Please consider an appropriate change to make this happen. --- diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 95181e36891a..b09c5b955555 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -4053,7 +4053,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_read_prepare); void ring_buffer_read_prepare_sync(void) { - synchronize_sched(); +// synchronize_sched(); } EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);