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 EBFCAC4332F for ; Wed, 1 Nov 2023 00:08:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344993AbjKAAIJ (ORCPT ); Tue, 31 Oct 2023 20:08:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38660 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231129AbjKAAIH (ORCPT ); Tue, 31 Oct 2023 20:08:07 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B72AF1 for ; Tue, 31 Oct 2023 17:07:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1698797238; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/XmSqIj8K+oPvNvHgr7ejZR9fz9xH8Hsy41r+CBGWQQ=; b=ACw7yr5M5FV5Umv+YFiTlSjuddjEica7IJPw59Z9j0pZpzONCginrEe8RsztMFu1Kw242Z GcMRDHnQRMz/iL1ytmMKsOzefaUjULxOkL9eEIB2dntkGDKqM1lh2drkFH2OfHuW/1js5k ngNM5GT23PakrluoxMKxgOeFgfObDF8= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-39-fBbDz5rDOJ6BmXSHnzoTaw-1; Tue, 31 Oct 2023 20:07:06 -0400 X-MC-Unique: fBbDz5rDOJ6BmXSHnzoTaw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id EF3453857B66; Wed, 1 Nov 2023 00:07:04 +0000 (UTC) Received: from [10.22.33.150] (unknown [10.22.33.150]) by smtp.corp.redhat.com (Postfix) with ESMTP id 90BD02026D4C; Wed, 1 Nov 2023 00:07:03 +0000 (UTC) Message-ID: <88ec9d43-2366-b885-d856-d87907afb820@redhat.com> Date: Tue, 31 Oct 2023 20:07:03 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.14.0 Subject: Re: [PATCH] rcu: Break rcu_node_0 --> &rq->__lock order Content-Language: en-US To: Peter Zijlstra , "Paul E. McKenney" Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , linux-kernel@vger.kernel.org, Phil Auld , kernel test robot , aubrey.li@linux.intel.com, yu.c.chen@intel.com, frederic@kernel.org, quic_neeraju@quicinc.com, joel@joelfernandes.org, josh@joshtriplett.org, boqun.feng@gmail.com, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, qiang.zhang1211@gmail.com References: <20231031001418.274187-1-longman@redhat.com> <20231031085308.GB35651@noisy.programming.kicks-ass.net> <20231031200228.GG15024@noisy.programming.kicks-ass.net> From: Waiman Long In-Reply-To: <20231031200228.GG15024@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.4 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/31/23 16:02, Peter Zijlstra wrote: > On Tue, Oct 31, 2023 at 07:29:04AM -0700, Paul E. McKenney wrote: >> Other than the de-alphabetization of the local variables, it looks >> plausible to me. Frederic's suggestion also sounds plausible to me. > Having spend the better part of the past two decades using upside down > xmas trees for local variables, this alphabet thing is obnoxious :-) > > But your code, your rules. > > To reduce the number of alphabet songs required, I've taken the liberty > to move a few variables into a narrower scope, hope that doesn't offend. > > --- > Subject: rcu: Break rcu_node_0 --> &rq->__lock order > From: Peter Zijlstra > Date: Tue, 31 Oct 2023 09:53:08 +0100 > > Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in > do_set_cpus_allowed()") added a kfree() call to free any user > provided affinity mask, if present. It was changed later to use > kfree_rcu() in commit 9a5418bc48ba ("sched/core: Use kfree_rcu() > in do_set_cpus_allowed()") to avoid a circular locking dependency > problem. > > It turns out that even kfree_rcu() isn't safe for avoiding > circular locking problem. As reported by kernel test robot, > the following circular locking dependency now exists: > > &rdp->nocb_lock --> rcu_node_0 --> &rq->__lock > > Solve this by breaking the rcu_node_0 --> &rq->__lock chain by moving > the resched_cpu() out from under rcu_node lock. > > [peterz: heavily borrowed from Waiman's Changelog] > Fixes: 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") > Reported-by: kernel test robot > Signed-off-by: Peter Zijlstra (Intel) > Link: https://lore.kernel.org/oe-lkp/202310302207.a25f1a30-oliver.sang@intel.com Thanks for addressing this issue. I am fine with your way as long as it gets the job done. I am not familiar enough of the RCU code to do a proper review, but I do get the general idea of your change and it looks good to me. Acked-by: Waiman Long > --- > kernel/rcu/tree.c | 34 ++++++++++++++++++++++++---------- > 1 file changed, 24 insertions(+), 10 deletions(-) > > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -754,14 +754,19 @@ static int dyntick_save_progress_counter > } > > /* > - * Return true if the specified CPU has passed through a quiescent > - * state by virtue of being in or having passed through an dynticks > - * idle state since the last call to dyntick_save_progress_counter() > - * for this same CPU, or by virtue of having been offline. > + * Returns positive if the specified CPU has passed through a quiescent state > + * by virtue of being in or having passed through an dynticks idle state since > + * the last call to dyntick_save_progress_counter() for this same CPU, or by > + * virtue of having been offline. > + * > + * Returns negative if the specified CPU needs a force resched. > + * > + * Returns zero otherwise. > */ > static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) > { > unsigned long jtsq; > + int ret = 0; > struct rcu_node *rnp = rdp->mynode; > > /* > @@ -847,8 +852,8 @@ static int rcu_implicit_dynticks_qs(stru > (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) || > rcu_state.cbovld)) { > WRITE_ONCE(rdp->rcu_urgent_qs, true); > - resched_cpu(rdp->cpu); > WRITE_ONCE(rdp->last_fqs_resched, jiffies); > + ret = -1; > } > > /* > @@ -891,7 +896,7 @@ static int rcu_implicit_dynticks_qs(stru > } > } > > - return 0; > + return ret; > } > > /* Trace-event wrapper function for trace_rcu_future_grace_period. */ > @@ -2257,15 +2262,15 @@ static void force_qs_rnp(int (*f)(struct > { > int cpu; > unsigned long flags; > - unsigned long mask; > - struct rcu_data *rdp; > struct rcu_node *rnp; > > rcu_state.cbovld = rcu_state.cbovldnext; > rcu_state.cbovldnext = false; > rcu_for_each_leaf_node(rnp) { > + unsigned long mask = 0; > + unsigned long rsmask = 0; > + > cond_resched_tasks_rcu_qs(); > - mask = 0; > raw_spin_lock_irqsave_rcu_node(rnp, flags); > rcu_state.cbovldnext |= !!rnp->cbovldmask; > if (rnp->qsmask == 0) { > @@ -2283,11 +2288,17 @@ static void force_qs_rnp(int (*f)(struct > continue; > } > for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) { > + struct rcu_data *rdp; > + int ret; > + > rdp = per_cpu_ptr(&rcu_data, cpu); > - if (f(rdp)) { > + ret = f(rdp); > + if (ret > 0) { > mask |= rdp->grpmask; > rcu_disable_urgency_upon_qs(rdp); > } > + if (ret < 0) > + rsmask |= rdp->grpmask; > } > if (mask != 0) { > /* Idle/offline CPUs, report (releases rnp->lock). */ > @@ -2296,6 +2307,9 @@ static void force_qs_rnp(int (*f)(struct > /* Nothing to do here, so just drop the lock. */ > raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > } > + > + for_each_leaf_node_cpu_mask(rnp, cpu, rsmask) > + resched_cpu(cpu); > } > } > >