From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932460Ab0KLPpO (ORCPT ); Fri, 12 Nov 2010 10:45:14 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:64646 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932323Ab0KLPpN (ORCPT ); Fri, 12 Nov 2010 10:45:13 -0500 X-Authority-Analysis: v=1.1 cv=+c36koQ5Dcj/1qolKHjtkYAGXvrVJRRiKMp+84F5sLg= c=1 sm=0 a=k53nsy2gcNIA:10 a=Q9fys5e9bTEA:10 a=OPBmh+XkhLl+Enan7BmTLg==:17 a=20KFwNOVAAAA:8 a=meVymXHHAAAA:8 a=pcCPffVJ2f5W7mNEU0oA:9 a=pJPsNrAjaPwj1GSoe-MA:7 a=l0HIUq57SYiX5e_0yVA3vG4KwrcA:4 a=PUjeQqilurYA:10 a=jEp0ucaQiEUA:10 a=jeBq3FmKZ4MA:10 a=OPBmh+XkhLl+Enan7BmTLg==:117 X-Cloudmark-Score: 0 X-Originating-IP: 67.242.120.143 Subject: Re: [PATCH 3/3] tracing: Fix recursive user stack trace From: Steven Rostedt To: Eric Dumazet Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Frederic Weisbecker , Jiri Olsa In-Reply-To: <1289575271.3185.256.camel@edumazet-laptop> References: <20101112151045.672405637@goodmis.org> <20101112151223.183540991@goodmis.org> <1289575271.3185.256.camel@edumazet-laptop> Content-Type: text/plain; charset="ISO-8859-15" Date: Fri, 12 Nov 2010 10:45:11 -0500 Message-ID: <1289576711.12418.401.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2010-11-12 at 16:21 +0100, Eric Dumazet wrote: > Le vendredi 12 novembre 2010 à 10:10 -0500, Steven Rostedt a écrit : > > pièce jointe document texte brut > > (0003-tracing-Fix-recursive-user-stack-trace.patch) > > From: Steven Rostedt > > > > The user stack trace can fault when examining the trace. Which > > would call the do_page_fault handler, which would trace again, > > which would do the user stack trace, which would fault and call > > do_page_fault again ... > > > > Thus this is causing a recursive bug. We need to have a recursion > > detector here. > > > > [ Resubmitted by Jiri Olsa ] > > Signed-off-by: Jiri Olsa > > LKML-Reference: <1289390172-9730-3-git-send-email-jolsa@redhat.com> > > Signed-off-by: Steven Rostedt > > --- > > kernel/trace/trace.c | 19 +++++++++++++++++++ > > 1 files changed, 19 insertions(+), 0 deletions(-) > > > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > > index 82d9b81..0215e87 100644 > > --- a/kernel/trace/trace.c > > +++ b/kernel/trace/trace.c > > @@ -1284,6 +1284,8 @@ void trace_dump_stack(void) > > __ftrace_trace_stack(global_trace.buffer, flags, 3, preempt_count()); > > } > > > > +static DEFINE_PER_CPU(int, user_stack_count); > > + > > void > > ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc) > > { > > @@ -1302,6 +1304,18 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc) > > if (unlikely(in_nmi())) > > return; > > > > + /* > > + * prevent recursion, since the user stack tracing may > > + * trigger other kernel events. > > + */ > > + preempt_disable(); > > + if (__get_cpu_var(user_stack_count)) > > + goto out; > > + > > if (__this_cpu_read(user_stack_count)) > goto out; > > > + __get_cpu_var(user_stack_count)++; > > __this_cpu_inc(user_stack_count); Thanks, I'll update and resubmit. -- Steve > > > + > > + > > + > > event = trace_buffer_lock_reserve(buffer, TRACE_USER_STACK, > > sizeof(*entry), flags, pc); > > if (!event) > > @@ -1319,6 +1333,11 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc) > > save_stack_trace_user(&trace); > > if (!filter_check_discard(call, entry, buffer, event)) > > ring_buffer_unlock_commit(buffer, event); > > + > > + __get_cpu_var(user_stack_count)--; > __this_cpu_dec(user_stack_count); > > > + > > + out: > > + preempt_enable(); > > } > > > > #ifdef UNUSED >