Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753115Ab3FNR1F (ORCPT ); Fri, 14 Jun 2013 13:27:05 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:40782 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752578Ab3FNR1D (ORCPT ); Fri, 14 Jun 2013 13:27:03 -0400 Date: Fri, 14 Jun 2013 10:25:16 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Masami Hiramatsu , "zhangwei(Jovi)" , Frederic Weisbecker , Ingo Molnar , Oleg Nesterov , Srikar Dronamraju , "linux-kernel@vger.kernel.org" , "yrl.pp-manager.tt@hitachi.com" Subject: Re: [PATCH] tracing/uprobes: Support ftrace_event_file base multibuffer Message-ID: <20130614172516.GP5146@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <51BA7578.4080108@huawei.com> <51BB18EB.9080307@hitachi.com> <1371223918.9844.324.camel@gandalf.local.home> <20130614162112.GO5146@linux.vnet.ibm.com> <1371227607.9844.335.camel@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1371227607.9844.335.camel@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13061417-5806-0000-0000-000021B6C4D4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1862 Lines: 47 On Fri, Jun 14, 2013 at 12:33:27PM -0400, Steven Rostedt wrote: > On Fri, 2013-06-14 at 09:21 -0700, Paul E. McKenney wrote: > > > > > > @@ -548,15 +556,35 @@ static void uprobe_trace_print(struct trace_uprobe *tu, > > > > > /* uprobe handler */ > > > > > static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs) > > > > > { > > > > > - if (!is_ret_probe(tu)) > > > > > - uprobe_trace_print(tu, 0, regs); > > > > > + struct ftrace_event_file **file; > > > > > + > > > > > + if (is_ret_probe(tu)) > > > > > + return 0; > > > > > + > > > > > + file = rcu_dereference_raw(tu->files); > > > > > > Why are you using rcu_dereference_raw() and not rcu_dereference(). The > > > _raw() is a bit special, and unless you know what you are doing with RCU > > > here, don't use it. > > > > > > As I see you using rcu_dereference_raw() all over this patch, along with > > > mutexes, I believe that you are not using RCU correctly here. > > > > If irqs and preempt are disabled, I suggest using rcu_dereference_sched(). > > That is what it is there for. ;-) > > I believe this just copied what kprobes did, where irqs and preemption > is disabled. I don't believe that these probes have that same luxury. > > But that begs the question. Should we convert the rcu_dereference_raw() > in the kprobe code to rcu_dereference_sched()? It makes a lot of sense to me, at least assuming no issues with the interrupts being disabled, but the checks not spotting this. Here is the check: preempt_count() != 0 || irqs_disabled() (With additional elaboration for if lockdep is enabled.) Thanx, Paul -- 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/