From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030197AbaLMK7m (ORCPT ); Sat, 13 Dec 2014 05:59:42 -0500 Received: from mail.skyhub.de ([78.46.96.112]:43923 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966436AbaLMK7k (ORCPT ); Sat, 13 Dec 2014 05:59:40 -0500 Date: Sat, 13 Dec 2014 11:59:25 +0100 From: Borislav Petkov To: Steven Rostedt Cc: Thomas Gleixner , LKML , Jiang Liu , x86@kernel.org, Linus Torvalds , Andrew Morton , Bjorn Helgaas , Tony Luck , Joerg Roedel , Marc Zyngier , Yinghai Lu , Alex Williamson Subject: Re: [RFC PATCH 2/2] tracing: Add tracepoint_printk cmdline Message-ID: <20141213105925.GB29934@pd.tnic> References: <20141212181420.47100d5c@gandalf.local.home> <20141213004830.792da019@gandalf.local.home> <20141213005037.78eca245@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20141213005037.78eca245@gandalf.local.home> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Dec 13, 2014 at 12:50:37AM -0500, Steven Rostedt wrote: > > Add the kernel command line tracepoint_printk option that will > have tracepoints that are active sent to printk(). > > Passing "tracepoint_printk" will activate this. To turn it off > the sysctl /proc/sys/kernel/tracepoint_printk can have '0' echoed > into it. Note, this only works if the cmdline option is used. > Echoing 1 into the sysctl file without the cmdline option will > have no affect. > > Note, this is a dangerous option. Having high frequency > tracepoints send their data to printk() can possibly cause > a live lock. > > Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1412121539300.16494@nanos > > Suggested-by: Thomas Gleixner > Signed-off-by: Steven Rostedt > --- > Documentation/kernel-parameters.txt | 18 ++++++++++++++++++ > include/linux/ftrace.h | 1 + > kernel/sysctl.c | 7 +++++++ > kernel/trace/trace.c | 17 +++++++++++++++++ > kernel/trace/trace.h | 1 + > kernel/trace/trace_events.c | 32 ++++++++++++++++++++++++++++++++ > 6 files changed, 76 insertions(+) > > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt > index 1d09eb37c562..d81f464a7358 100644 > --- a/Documentation/kernel-parameters.txt > +++ b/Documentation/kernel-parameters.txt > @@ -3500,6 +3500,24 @@ bytes respectively. Such letter suffixes can also be entirely omitted. > See also Documentation/trace/ftrace.txt "trace options" > section. > > + tracepoint_printk[FTRACE] Damn, this is long and most likely nasty to type on some dingy box when you're trying to debug stuff. Can we shorten it? trace_printk tp_printk tp_print tp_pr ... Last one is my favourite - we should call it ToiletPaper_Print :-) > + Have the tracepoints sent to printk as well as the > + tracing ring buffer. This is useful for early boot up > + where the system hangs or reboots and does not give the > + option for reading the tracing buffer or performing a > + ftrace_dump_on_oops. -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. --