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 666FEC433FE for ; Fri, 14 Oct 2022 14:39:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229885AbiJNOjG (ORCPT ); Fri, 14 Oct 2022 10:39:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59026 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229711AbiJNOjD (ORCPT ); Fri, 14 Oct 2022 10:39:03 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6B14F1D4DE7; Fri, 14 Oct 2022 07:39:02 -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 ams.source.kernel.org (Postfix) with ESMTPS id 071EFB82355; Fri, 14 Oct 2022 14:39:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6641FC433C1; Fri, 14 Oct 2022 14:38:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1665758339; bh=+/LWxZHh5+rRSm5v/5u0km05gGmDmFBODsWnb/6k6tU=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=P08OpAutKf29WIlDc5S/eE47g3hC3PMTlRUK4Ui5gqyEfdcNbIQSl6Zn4Z/9XfIOj eU8iHpgP12yvQLG69GZhFOZJIO9VcWaCV+WoATpkYOWO5vQtk5TysceSXi+NOuJ1kL /BYV4LilxplMG94gGFYBEbVPEP3S/9ve97/ceeM1BD72RnwMiBsSmmmDUSwo/xWWJU 1v8ts9lprfm0MD3Tvdj4gln1ekMUmRYeBZ/2EGmX+Prbka2gKZYx96YsNasl6DkhNR 3mDuFKUMCNgqD+SRmKAhNb/zKn6Egx3TXZeGn46HP4/ittlnGB11L4/0hXVaDncRZo 0uHPuriTKWoVQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 49EB05C32BF; Fri, 14 Oct 2022 07:38:56 -0700 (PDT) Date: Fri, 14 Oct 2022 07:38:56 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: Zqiang , frederic@kernel.org, quic_neeraju@quicinc.com, rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] rcu: Fix use __this_cpu_read() warning in preemptible code Message-ID: <20221014143856.GF4221@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20221013044148.2894320-1-qiang1.zhang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 13, 2022 at 03:39:45PM +0000, Joel Fernandes wrote: > On Thu, Oct 13, 2022 at 12:41:48PM +0800, Zqiang wrote: > > BUG: using __this_cpu_read() in preemptible [00000000] > > code: rcu_torture_fqs/398 > > caller is __this_cpu_preempt_check+0x13/0x20 > > CPU: 3 PID: 398 Comm: rcu_torture_fqs Not tainted 6.0.0-rc1-yoctodev-standard+ > > Call Trace: > > > > dump_stack_lvl+0x5b/0x86 > > dump_stack+0x10/0x16 > > check_preemption_disabled+0xe5/0xf0 > > __this_cpu_preempt_check+0x13/0x20 > > rcu_force_quiescent_state.part.0+0x1c/0x170 > > rcu_force_quiescent_state+0x1e/0x30 > > rcu_torture_fqs+0xca/0x160 > > ? rcu_torture_boost+0x430/0x430 > > kthread+0x192/0x1d0 > > ? kthread_complete_and_exit+0x30/0x30 > > ret_from_fork+0x22/0x30 > > > > > > When enable rcutorture.fqs_duration, the rcu_force_quiescent_state() be > > invoked in rcu_torture_fqs task context, invoke __this_cpu_read() in > > preemptible code section will trigger the above calltrace. > > Makes sense, so in theory the GP thread might get migrated after sampling > rcu_data.mynode but that's Ok since it wont change the behavior of the code > following it AFAICS. > > Reviewed-by: Joel Fernandes (Google) Thank you! I will apply this on the next rebase. Thanx, Paul > thanks, > > - Joel > > > This commit convert __this_cpu_read() to raw_cpu_read() to avoid > > this warning. > > > > Signed-off-by: Zqiang > > --- > > kernel/rcu/tree.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index 96d678c9cfb6..282002e62cf3 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -2436,7 +2436,7 @@ void rcu_force_quiescent_state(void) > > struct rcu_node *rnp_old = NULL; > > > > /* Funnel through hierarchy to reduce memory contention. */ > > - rnp = __this_cpu_read(rcu_data.mynode); > > + rnp = raw_cpu_read(rcu_data.mynode); > > for (; rnp != NULL; rnp = rnp->parent) { > > ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) || > > !raw_spin_trylock(&rnp->fqslock); > > -- > > 2.25.1 > >