From nobody Mon Sep 8 08:57:30 2025 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 355AEC6FA8A for ; Tue, 13 Sep 2022 15:05:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235260AbiIMPFw (ORCPT ); Tue, 13 Sep 2022 11:05:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41850 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235281AbiIMPD5 (ORCPT ); Tue, 13 Sep 2022 11:03:57 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 60D9427CEF; Tue, 13 Sep 2022 07:29:56 -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 81647B80F62; Tue, 13 Sep 2022 14:29:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EF4E9C433D6; Tue, 13 Sep 2022 14:29:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1663079379; bh=wrCLvSaAPaEWFtV09hkme+TgSL67YREqg4eTQhNtS8M=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SLIJcjReA2iYbH3Y8M5gqRiKDwJmj0w5nIpjYLMQT1PieGBYM6gK/mT24FIX49nRC Hf1kVrgiOps1RhRLauUrJ04iwc3n6aPv04CCrt8d7ppn12uqoSIctiIqmUDzttmVhl xjI/ixKZ3fR3Is7SQNAkkxizq+F5sLLvnC4oZehE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tejun Heo , Sasha Levin , Imran Khan , Xuewen Yan Subject: [PATCH 5.4 087/108] cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock Date: Tue, 13 Sep 2022 16:06:58 +0200 Message-Id: <20220913140357.359330349@linuxfoundation.org> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20220913140353.549108748@linuxfoundation.org> References: <20220913140353.549108748@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Tejun Heo [ Upstream commit 4f7e7236435ca0abe005c674ebd6892c6e83aeb3 ] Bringing up a CPU may involve creating and destroying tasks which requires read-locking threadgroup_rwsem, so threadgroup_rwsem nests inside cpus_read_lock(). However, cpuset's ->attach(), which may be called with thredagroup_rwsem write-locked, also wants to disable CPU hotplug and acquires cpus_read_lock(), leading to a deadlock. Fix it by guaranteeing that ->attach() is always called with CPU hotplug disabled and removing cpus_read_lock() call from cpuset_attach(). Signed-off-by: Tejun Heo Reviewed-and-tested-by: Imran Khan Reported-and-tested-by: Xuewen Yan Fixes: 05c7b7a92cc8 ("cgroup/cpuset: Fix a race between cpuset_attach() and= cpu hotplug") Cc: stable@vger.kernel.org # v5.17+ Signed-off-by: Sasha Levin --- kernel/cgroup/cgroup.c | 78 ++++++++++++++++++++++++++++++++++----------= ----- kernel/cgroup/cpuset.c | 3 - 2 files changed, 56 insertions(+), 25 deletions(-) --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -30,6 +30,7 @@ =20 #include "cgroup-internal.h" =20 +#include #include #include #include @@ -2377,6 +2378,47 @@ int task_cgroup_path(struct task_struct EXPORT_SYMBOL_GPL(task_cgroup_path); =20 /** + * cgroup_attach_lock - Lock for ->attach() + * @lock_threadgroup: whether to down_write cgroup_threadgroup_rwsem + * + * cgroup migration sometimes needs to stabilize threadgroups against fork= s and + * exits by write-locking cgroup_threadgroup_rwsem. However, some ->attach= () + * implementations (e.g. cpuset), also need to disable CPU hotplug. + * Unfortunately, letting ->attach() operations acquire cpus_read_lock() c= an + * lead to deadlocks. + * + * Bringing up a CPU may involve creating and destroying tasks which requi= res + * read-locking threadgroup_rwsem, so threadgroup_rwsem nests inside + * cpus_read_lock(). If we call an ->attach() which acquires the cpus lock= while + * write-locking threadgroup_rwsem, the locking order is reversed and we e= nd up + * waiting for an on-going CPU hotplug operation which in turn is waiting = for + * the threadgroup_rwsem to be released to create new tasks. For more deta= ils: + * + * http://lkml.kernel.org/r/20220711174629.uehfmqegcwn2lqzu@wubuntu + * + * Resolve the situation by always acquiring cpus_read_lock() before optio= nally + * write-locking cgroup_threadgroup_rwsem. This allows ->attach() to assum= e that + * CPU hotplug is disabled on entry. + */ +static void cgroup_attach_lock(bool lock_threadgroup) +{ + cpus_read_lock(); + if (lock_threadgroup) + percpu_down_write(&cgroup_threadgroup_rwsem); +} + +/** + * cgroup_attach_unlock - Undo cgroup_attach_lock() + * @lock_threadgroup: whether to up_write cgroup_threadgroup_rwsem + */ +static void cgroup_attach_unlock(bool lock_threadgroup) +{ + if (lock_threadgroup) + percpu_up_write(&cgroup_threadgroup_rwsem); + cpus_read_unlock(); +} + +/** * cgroup_migrate_add_task - add a migration target task to a migration co= ntext * @task: target task * @mgctx: target migration context @@ -2857,8 +2899,7 @@ int cgroup_attach_task(struct cgroup *ds } =20 struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup, - bool *locked) - __acquires(&cgroup_threadgroup_rwsem) + bool *threadgroup_locked) { struct task_struct *tsk; pid_t pid; @@ -2875,12 +2916,8 @@ struct task_struct *cgroup_procs_write_s * Therefore, we can skip the global lock. */ lockdep_assert_held(&cgroup_mutex); - if (pid || threadgroup) { - percpu_down_write(&cgroup_threadgroup_rwsem); - *locked =3D true; - } else { - *locked =3D false; - } + *threadgroup_locked =3D pid || threadgroup; + cgroup_attach_lock(*threadgroup_locked); =20 rcu_read_lock(); if (pid) { @@ -2911,17 +2948,14 @@ struct task_struct *cgroup_procs_write_s goto out_unlock_rcu; =20 out_unlock_threadgroup: - if (*locked) { - percpu_up_write(&cgroup_threadgroup_rwsem); - *locked =3D false; - } + cgroup_attach_unlock(*threadgroup_locked); + *threadgroup_locked =3D false; out_unlock_rcu: rcu_read_unlock(); return tsk; } =20 -void cgroup_procs_write_finish(struct task_struct *task, bool locked) - __releases(&cgroup_threadgroup_rwsem) +void cgroup_procs_write_finish(struct task_struct *task, bool threadgroup_= locked) { struct cgroup_subsys *ss; int ssid; @@ -2929,8 +2963,8 @@ void cgroup_procs_write_finish(struct ta /* release reference from cgroup_procs_write_start() */ put_task_struct(task); =20 - if (locked) - percpu_up_write(&cgroup_threadgroup_rwsem); + cgroup_attach_unlock(threadgroup_locked); + for_each_subsys(ss, ssid) if (ss->post_attach) ss->post_attach(); @@ -3007,8 +3041,7 @@ static int cgroup_update_dfl_csses(struc * write-locking can be skipped safely. */ has_tasks =3D !list_empty(&mgctx.preloaded_src_csets); - if (has_tasks) - percpu_down_write(&cgroup_threadgroup_rwsem); + cgroup_attach_lock(has_tasks); =20 /* NULL dst indicates self on default hierarchy */ ret =3D cgroup_migrate_prepare_dst(&mgctx); @@ -3029,8 +3062,7 @@ static int cgroup_update_dfl_csses(struc ret =3D cgroup_migrate_execute(&mgctx); out_finish: cgroup_migrate_finish(&mgctx); - if (has_tasks) - percpu_up_write(&cgroup_threadgroup_rwsem); + cgroup_attach_unlock(has_tasks); return ret; } =20 @@ -4859,13 +4891,13 @@ static ssize_t cgroup_procs_write(struct struct task_struct *task; const struct cred *saved_cred; ssize_t ret; - bool locked; + bool threadgroup_locked; =20 dst_cgrp =3D cgroup_kn_lock_live(of->kn, false); if (!dst_cgrp) return -ENODEV; =20 - task =3D cgroup_procs_write_start(buf, true, &locked); + task =3D cgroup_procs_write_start(buf, true, &threadgroup_locked); ret =3D PTR_ERR_OR_ZERO(task); if (ret) goto out_unlock; @@ -4891,7 +4923,7 @@ static ssize_t cgroup_procs_write(struct ret =3D cgroup_attach_task(dst_cgrp, task, true); =20 out_finish: - cgroup_procs_write_finish(task, locked); + cgroup_procs_write_finish(task, threadgroup_locked); out_unlock: cgroup_kn_unlock(of->kn); =20 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2204,7 +2204,7 @@ static void cpuset_attach(struct cgroup_ cgroup_taskset_first(tset, &css); cs =3D css_cs(css); =20 - cpus_read_lock(); + lockdep_assert_cpus_held(); /* see cgroup_attach_lock() */ percpu_down_write(&cpuset_rwsem); =20 /* prepare for attach */ @@ -2260,7 +2260,6 @@ static void cpuset_attach(struct cgroup_ wake_up(&cpuset_attach_wq); =20 percpu_up_write(&cpuset_rwsem); - cpus_read_unlock(); } =20 /* The various types of files and directories in a cpuset file system */