From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755834AbbKRNLz (ORCPT ); Wed, 18 Nov 2015 08:11:55 -0500 Received: from mail.efficios.com ([78.47.125.74]:59327 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755749AbbKRNLy (ORCPT ); Wed, 18 Nov 2015 08:11:54 -0500 Date: Wed, 18 Nov 2015 13:11:45 +0000 (UTC) From: Mathieu Desnoyers To: masami hiramatsu pt Cc: rostedt , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , LKML Message-ID: <410834711.113922.1447852305905.JavaMail.zimbra@efficios.com> In-Reply-To: <50399556C9727B4D88A595C8584AAB375262179B@GSjpTKYDCembx32.service.hitachi.net> References: <559989072.111063.1447778135704.JavaMail.zimbra@efficios.com> <20151117122333.71f5a903@gandalf.local.home> <50399556C9727B4D88A595C8584AAB375262179B@GSjpTKYDCembx32.service.hitachi.net> Subject: Re: trace: trace_kprobe.c always shows interrupts off MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [78.47.125.74] X-Mailer: Zimbra 8.6.0_GA_1178 (ZimbraWebClient - FF42 (Linux)/8.6.0_GA_1178) Thread-Topic: trace: trace_kprobe.c always shows interrupts off Thread-Index: AdEhq+ZM8rQ1HuWuRfOx6AsyzKW/RY/wUF7I Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Nov 18, 2015, at 1:51 AM, masami hiramatsu pt masami.hiramatsu.pt@hitachi.com wrote: > Hi Mathieu, Steven, > > From: Steven Rostedt [mailto:rostedt@goodmis.org] >> >>On Tue, 17 Nov 2015 16:35:35 +0000 (UTC) >>Mathieu Desnoyers wrote: >> >>> Hi, >>> >>> I notice that trace_kprobe.c does local_save_flags() within >>> __kprobe_trace_func(), which is called (at least on x86) with >>> interrupts always disabled. This is then used as interrupt on/off >>> state within the recorded event, which is misleading. >> >>Kinda. The kprobe itself has interrupts disabled, so it's only a white >>lie. >> >>> >>> I also don't understand why arch/x86/kernel/kprobes/ftrace.c >>> pre handler disables interrupts, considering the following >>> comment above arch/x86/kernel/kprobes/core.c: kprobe_int3_handler() >>> >>> * Interrupts are disabled on entry as trap3 is an interrupt gate and they >>> * remain disabled throughout this function. >> >>I think you answered your own question. The key piece you may be >>missing is that kprobe_ftrace_handler() is not called from a trap, but >>from a function traced callback, which does not disable interrupts. > > right, since the user can not forcibly change any kprobes to > jump, those handlers should be ran under the same environment. > >>> A struct pt_regs is received by this function, but I don't see >>> any way to get the state of irq enable/disable from struct pt_regs >>> across architectures. >>> >>> Any thoughts on how to fix this ? >> >>Create a cross arch: flags = regs_irq_save(regs) function. >> > > Good idea! Anyway, we can start on x86, in other arch we can > prepare a dummy function to return current interrupt state(as > we are doing now). Derived from Steven's idea, I added a lttng_regs_irqs_disabled(struct pt_regs *regs) to lttng-modules. The generic version returns "-1", which means that the architecture don't support it yet. It returns 1 or 0 when implemented. I prefer this approach compared to fall-back to irqs_disabled(), because users then know that they can trust the information when it is available. Returning an unknown state with a regs_irq_save(regs) did not seem obvious, because there is no guarantee that a value like "-1" does not mean something specific on some architectures. One possibility would be to make it return success/failure, and populate the flags in an output parameter, but that seems rather cumbersome. When regs_irq_save() becomes widely available across architectures in newer kernels, I'll use it of course. Thanks, Mathieu > > Thank you, > > ---- > Masami Hiramatsu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com