From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 63E7AC433F5 for ; Mon, 16 May 2022 11:49:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240174AbiEPLtf (ORCPT ); Mon, 16 May 2022 07:49:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36442 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229890AbiEPLt3 (ORCPT ); Mon, 16 May 2022 07:49:29 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 12B2FDF8D; Mon, 16 May 2022 04:49:26 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 72A1660FFC; Mon, 16 May 2022 11:49:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5281AC385B8; Mon, 16 May 2022 11:49:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1652701765; bh=1UjUf9qgR8mCHZ9pO5ibdXOTkA+2CnwKyYDerjjSjGA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gMkYxYwaD2K0qgkQWrvFjMbEes4kia98EUUVJ/06WXfRTmnyYFI3+clNVoLAQu0/F x+63icf6hFCM/xsO/+YqetIoB4x1gBd+Q0z+jkU58s/KBV5u+gOj1DguI8HjQPFHZJ vvpflzD8mQqRkZEtvS5uJxpZqREmSgXWpzXkSehLhvHWGXMoA0snQrvlWtBU+MRVd8 Io7mXMB4rZKJVMePun91CFyq/qLWre8LzQ/Tr8EnQ5HwsN8K0vwCBskWRAyJi2LT75 IWBDOZ/t+kz0pTa6dUeW24jK/LLmqV9hPJLuMxUa4YMiCFSYw1elIzxapFohDrxy+r 75pBVqDXWPFjg== Date: Mon, 16 May 2022 13:49:22 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: Jiri Olsa , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Masami Hiramatsu , netdev@vger.kernel.org, bpf@vger.kernel.org, lkml , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Steven Rostedt Subject: Re: [PATCH bpf-next 1/2] cpuidle/rcu: Making arch_cpu_idle and rcu_idle_exit noinstr Message-ID: <20220516114922.GA349949@lothringen> References: <20220515203653.4039075-1-jolsa@kernel.org> <20220516042535.GV1790663@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220516042535.GV1790663@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, May 15, 2022 at 09:25:35PM -0700, Paul E. McKenney wrote: > On Sun, May 15, 2022 at 10:36:52PM +0200, Jiri Olsa wrote: > > Making arch_cpu_idle and rcu_idle_exit noinstr. Both functions run > > in rcu 'not watching' context and if there's tracer attached to > > them, which uses rcu (e.g. kprobe multi interface) it will hit RCU > > warning like: > > > > [ 3.017540] WARNING: suspicious RCU usage > > ... > > [ 3.018363] kprobe_multi_link_handler+0x68/0x1c0 > > [ 3.018364] ? kprobe_multi_link_handler+0x3e/0x1c0 > > [ 3.018366] ? arch_cpu_idle_dead+0x10/0x10 > > [ 3.018367] ? arch_cpu_idle_dead+0x10/0x10 > > [ 3.018371] fprobe_handler.part.0+0xab/0x150 > > [ 3.018374] 0xffffffffa00080c8 > > [ 3.018393] ? arch_cpu_idle+0x5/0x10 > > [ 3.018398] arch_cpu_idle+0x5/0x10 > > [ 3.018399] default_idle_call+0x59/0x90 > > [ 3.018401] do_idle+0x1c3/0x1d0 > > > > The call path is following: > > > > default_idle_call > > rcu_idle_enter > > arch_cpu_idle > > rcu_idle_exit > > > > The arch_cpu_idle and rcu_idle_exit are the only ones from above > > path that are traceble and cause this problem on my setup. > > > > Signed-off-by: Jiri Olsa > > From an RCU viewpoint: > > Reviewed-by: Paul E. McKenney > > [ I considered asking for an instrumentation_on() in rcu_idle_exit(), > but there is no point given that local_irq_restore() isn't something > you instrument anyway. ] So local_irq_save() in the beginning of rcu_idle_exit() is unsafe because it is instrumentable by the function (graph) tracers and the irqsoff tracer. Also it calls into lockdep that might make use of RCU. That's why rcu_idle_exit() is not noinstr yet. See this patch: https://lore.kernel.org/lkml/20220503100051.2799723-4-frederic@kernel.org/ Thanks. > > > --- > > arch/x86/kernel/process.c | 2 +- > > kernel/rcu/tree.c | 2 +- > > 2 files changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c > > index b370767f5b19..1345cb0124a6 100644 > > --- a/arch/x86/kernel/process.c > > +++ b/arch/x86/kernel/process.c > > @@ -720,7 +720,7 @@ void arch_cpu_idle_dead(void) > > /* > > * Called from the generic idle code. > > */ > > -void arch_cpu_idle(void) > > +void noinstr arch_cpu_idle(void) > > { > > x86_idle(); > > } > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index a4b8189455d5..20d529722f51 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -896,7 +896,7 @@ static void noinstr rcu_eqs_exit(bool user) > > * If you add or remove a call to rcu_idle_exit(), be sure to test with > > * CONFIG_RCU_EQS_DEBUG=y. > > */ > > -void rcu_idle_exit(void) > > +void noinstr rcu_idle_exit(void) > > { > > unsigned long flags; > > > > -- > > 2.35.3 > >