From nobody Mon Jun 22 21:34:58 2026 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 E920CC433EF for ; Wed, 16 Mar 2022 17:43:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353447AbiCPRon (ORCPT ); Wed, 16 Mar 2022 13:44:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59618 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355558AbiCPRok (ORCPT ); Wed, 16 Mar 2022 13:44:40 -0400 Received: from fieldses.org (fieldses.org [IPv6:2600:3c00:e000:2f7::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 252D717046 for ; Wed, 16 Mar 2022 10:43:25 -0700 (PDT) Received: by fieldses.org (Postfix, from userid 2815) id 1CD1648F; Wed, 16 Mar 2022 13:43:24 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.11.0 fieldses.org 1CD1648F DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fieldses.org; s=default; t=1647452604; bh=Wl8eLmn2EyVMIbzbpeaNnxsMHJboV9nFjzpk/4KzOkE=; h=Date:To:Cc:Subject:From:From; b=zBBxlsA1m1y04DG77zWHK91zWwZexpegElKCeRRQsAAOGVz6jkaRT4Y43z0tHKno0 ZbEWWlpkHiM5RaWK4xfrJMEwtApTqrkUtJ91AFw/+uLgUfHBkRoDUS6MR6k2rG1mMv u9zB9cXONokvgYmVbxprMe628XN95oMI3ESiscUE= Date: Wed, 16 Mar 2022 13:43:24 -0400 To: Chengming Zhou Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org Subject: failure to boot after dc6e0818bc9a "sched/cpuacct: Optimize away RCU read lock" Message-ID: <20220316174324.GA16511@fieldses.org> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) From: bfields@fieldses.org (J. Bruce Fields) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" One of my test VMs has been failing to boot linux-next recently. I finally got around to a bisect this morning, and it landed on the below. What other information would be useful to debug this? --b. commit dc6e0818bc9a Author: Chengming Zhou Date: Sun Feb 20 13:14:25 2022 +0800 sched/cpuacct: Optimize away RCU read lock =20 Since cpuacct_charge() is called from the scheduler update_curr(), we must already have rq lock held, then the RCU read lock can be optimized away. =20 And do the same thing in it's wrapper cgroup_account_cputime(), but we can't use lockdep_assert_rq_held() there, which defined in kernel/sched/sched.h. =20 Suggested-by: Peter Zijlstra (Intel) Signed-off-by: Chengming Zhou Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20220220051426.5274-2-zhouchengming@byt= edance.com diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 75c151413fda..9a109c6ac0e0 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -791,11 +791,9 @@ static inline void cgroup_account_cputime(struct task_= struct *task, =20 cpuacct_charge(task, delta_exec); =20 - rcu_read_lock(); cgrp =3D task_dfl_cgroup(task); if (cgroup_parent(cgrp)) __cgroup_account_cputime(cgrp, delta_exec); - rcu_read_unlock(); } =20 static inline void cgroup_account_cputime_field(struct task_struct *task, diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c index 307800586ac8..f79f88456d72 100644 --- a/kernel/sched/cpuacct.c +++ b/kernel/sched/cpuacct.c @@ -337,12 +337,10 @@ void cpuacct_charge(struct task_struct *tsk, u64 cput= ime) unsigned int cpu =3D task_cpu(tsk); struct cpuacct *ca; =20 - rcu_read_lock(); + lockdep_assert_rq_held(cpu_rq(cpu)); =20 for (ca =3D task_ca(tsk); ca; ca =3D parent_ca(ca)) *per_cpu_ptr(ca->cpuusage, cpu) +=3D cputime; - - rcu_read_unlock(); } =20 /*