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 X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62746C433DF for ; Wed, 3 Jun 2020 16:46:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 348CE20738 for ; Wed, 3 Jun 2020 16:46:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591202763; bh=9BGeS3aIurEa9XCCSdezzTD/sLkaxvXZa0S+eeu2Wbs=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=XDrcfjDledodWcn5fYq89m1B99aN+ZLqbLCthoVM4Fi/4Ak8Vf1qUEHx2ce3MIFRf xZNsvfamrZiniUR0nro+UzZwA4yJhH1DvF3kMNuN2ASml0d+wA8U7TzEROgrfVntoR zzQ1pv89TcS8/ap61Wze872xBaLbzy5WR64aGiS0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726147AbgFCQqC (ORCPT ); Wed, 3 Jun 2020 12:46:02 -0400 Received: from mail.kernel.org ([198.145.29.99]:48514 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725854AbgFCQqB (ORCPT ); Wed, 3 Jun 2020 12:46:01 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EBE36206A2; Wed, 3 Jun 2020 16:46:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591202761; bh=9BGeS3aIurEa9XCCSdezzTD/sLkaxvXZa0S+eeu2Wbs=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=mJ+0NmXzdDSeoeM4zZDEkBJ+wBZeEfrY95K1kWex6pMplWUl/cJL7BXw67VgZPRI2 PgYYXeAaOL//NlzlQdNhFy4Ipzm8qQ0jDg5Qp/mj7EpY8ZwderyBZ19WovVyLEBefo HtlvbFESFqQTqIYO5nmvt4Ahp851zsDXc/X6Kh3Y= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 750D335209C5; Wed, 3 Jun 2020 09:46:00 -0700 (PDT) Date: Wed, 3 Jun 2020 09:46:00 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: tglx@linutronix.de, x86@kernel.org, elver@google.com, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, will@kernel.org, dvyukov@google.com, glider@google.com, andreyknvl@google.com Subject: Re: [PATCH 2/9] rcu: Fixup noinstr warnings Message-ID: <20200603164600.GQ29598@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200603114014.152292216@infradead.org> <20200603114051.896465666@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200603114051.896465666@infradead.org> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 03, 2020 at 01:40:16PM +0200, Peter Zijlstra wrote: > A KCSAN build revealed we have explicit annoations through atomic_*() > usage, switch to arch_atomic_*() for the respective functions. > > vmlinux.o: warning: objtool: rcu_nmi_exit()+0x4d: call to __kcsan_check_access() leaves .noinstr.text section > vmlinux.o: warning: objtool: rcu_dynticks_eqs_enter()+0x25: call to __kcsan_check_access() leaves .noinstr.text section > vmlinux.o: warning: objtool: rcu_nmi_enter()+0x4f: call to __kcsan_check_access() leaves .noinstr.text section > vmlinux.o: warning: objtool: rcu_dynticks_eqs_exit()+0x2a: call to __kcsan_check_access() leaves .noinstr.text section > vmlinux.o: warning: objtool: __rcu_is_watching()+0x25: call to __kcsan_check_access() leaves .noinstr.text section > > Signed-off-by: Peter Zijlstra (Intel) > Link: https://lkml.kernel.org/r/20200603084818.GB2627@hirez.programming.kicks-ass.net > --- > kernel/rcu/tree.c | 11 +++++------ > 1 file changed, 5 insertions(+), 6 deletions(-) > > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -250,7 +250,7 @@ static noinstr void rcu_dynticks_eqs_ent > * next idle sojourn. > */ > rcu_dynticks_task_trace_enter(); // Before ->dynticks update! > - seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); > + seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); To preserve KCSAN's ability to see this, there would be something like instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks)) prior to the instrumentation_end() invoked before rcu_dynticks_eqs_enter() in each of rcu_eqs_enter() and rcu_nmi_exit(), correct? > // RCU is no longer watching. Better be in extended quiescent state! > WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && > (seq & RCU_DYNTICK_CTRL_CTR)); > @@ -274,13 +274,13 @@ static noinstr void rcu_dynticks_eqs_exi > * and we also must force ordering with the next RCU read-side > * critical section. > */ > - seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); > + seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); And same here, but after the instrumentation_begin() following rcu_dynticks_eqs_exit() in both rcu_eqs_exit() and rcu_nmi_enter(), correct? > // RCU is now watching. Better not be in an extended quiescent state! > rcu_dynticks_task_trace_exit(); // After ->dynticks update! > WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && > !(seq & RCU_DYNTICK_CTRL_CTR)); > if (seq & RCU_DYNTICK_CTRL_MASK) { > - atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks); > + arch_atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks); This one is gone in -rcu. > smp_mb__after_atomic(); /* _exit after clearing mask. */ > } > } > @@ -313,7 +313,7 @@ static __always_inline bool rcu_dynticks > { > struct rcu_data *rdp = this_cpu_ptr(&rcu_data); > > - return !(atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR); > + return !(arch_atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR); Also instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks)) as follows: o rcu_nmi_exit(): After each following instrumentation_begin(). o In theory in rcu_irq_exit_preempt(), but as this generates code only in lockdep builds, it might not be worth worrying about. o Ditto for rcu_irq_exit_check_preempt(). o Ditto for __rcu_irq_enter_check_tick(). o rcu_nmi_enter(): After each following instrumentation_begin(). o __rcu_is_watching() is itself noinstr: o idtentry_enter_cond_rcu(): After each following instrumentation_begin(). o rcu_is_watching(): Either before or after the call to rcu_dynticks_curr_cpu_in_eqs(). > } > > /* > @@ -692,6 +692,7 @@ noinstr void rcu_nmi_exit(void) > { > struct rcu_data *rdp = this_cpu_ptr(&rcu_data); > > + instrumentation_begin(); > /* > * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks. > * (We are exiting an NMI handler, so RCU better be paying attention > @@ -705,7 +706,6 @@ noinstr void rcu_nmi_exit(void) > * leave it in non-RCU-idle state. > */ > if (rdp->dynticks_nmi_nesting != 1) { > - instrumentation_begin(); > trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, > atomic_read(&rdp->dynticks)); > WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */ > @@ -714,7 +714,6 @@ noinstr void rcu_nmi_exit(void) > return; > } > > - instrumentation_begin(); > /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ > trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks)); > WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */ This one looks to be having no effect on instrumentation of atomics, but rather coalescing a pair of instrumentation_begin() into one. Do I understand correctly? Thanx, Paul