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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT 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 CA36AC76195 for ; Fri, 19 Jul 2019 14:00:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A03AB21851 for ; Fri, 19 Jul 2019 14:00:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729692AbfGSOAt (ORCPT ); Fri, 19 Jul 2019 10:00:49 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:36929 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729620AbfGSOAk (ORCPT ); Fri, 19 Jul 2019 10:00:40 -0400 Received: by mail-wr1-f67.google.com with SMTP id n9so7309798wrr.4 for ; Fri, 19 Jul 2019 07:00:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=lsvQwVtOgqTUPEZWlzxyNtyD9+2FMdmqdnW4Yq0lblc=; b=Jn3vt/p/Abtv4XknHecnrdLS5p4LcIDpC2JRj3cLeSP0Yd+ma1Eu6ZbRUWoIIl+U+g 4qb+BmmpWJa6bpLsh3uhchFVOTmk/ZxrvJVbseVmpxXTs5+JrOIZiALP3bDrtZoHqRbX 7bYAj/wxVCYVLKEMNJXyW5fA0D93ilSdaXo68Z40SY4sfcJj4NfYiJkjis1XlrtGwHRR wrEzE6bHA6/CvIA3tQW5GK4v9Nb+nLMmnnEqaBTaY1iWopOY+WGWh9LXmU42agDwlVbw oG4qDL7cBITZ/U7MfoHz50cHRokuAK8gO7aDtXkMOytWmkI6iwnHZhIpzzo3rI/Vcvse NCBw== X-Gm-Message-State: APjAAAUcckDloJ2V7PP/TOO3rsWOZxQ4pjEnXfzDbAQhAv+6TaH/gmxK +yl7Fqn5I/9pHFc/EXkjd38CvA== X-Google-Smtp-Source: APXvYqzSBmD3MlViISjR5eO2sNm4aBb2z24XYj7Sx+4ZvTUQDCsTaNLIALe5WYSOTXmeVW+jwd9RIA== X-Received: by 2002:adf:dc51:: with SMTP id m17mr31931061wrj.256.1563544837883; Fri, 19 Jul 2019 07:00:37 -0700 (PDT) Received: from localhost.localdomain.com ([151.15.230.231]) by smtp.gmail.com with ESMTPSA id f10sm21276926wrs.22.2019.07.19.07.00.36 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 19 Jul 2019 07:00:37 -0700 (PDT) From: Juri Lelli To: peterz@infradead.org, mingo@redhat.com, rostedt@goodmis.org, tj@kernel.org Cc: linux-kernel@vger.kernel.org, luca.abeni@santannapisa.it, claudio@evidence.eu.com, tommaso.cucinotta@santannapisa.it, bristot@redhat.com, mathieu.poirier@linaro.org, lizefan@huawei.com, longman@redhat.com, dietmar.eggemann@arm.com, cgroups@vger.kernel.org, Juri Lelli Subject: [PATCH v9 8/8] sched/core: Prevent race condition between cpuset and __sched_setscheduler() Date: Fri, 19 Jul 2019 16:00:00 +0200 Message-Id: <20190719140000.31694-9-juri.lelli@redhat.com> X-Mailer: git-send-email 2.17.2 In-Reply-To: <20190719140000.31694-1-juri.lelli@redhat.com> References: <20190719140000.31694-1-juri.lelli@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org No synchronisation mechanism exists between the cpuset subsystem and calls to function __sched_setscheduler(). As such, it is possible that new root domains are created on the cpuset side while a deadline acceptance test is carried out in __sched_setscheduler(), leading to a potential oversell of CPU bandwidth. Grab cpuset_rwsem read lock from core scheduler, so to prevent situations such as the one described above from happening. The only exception is normalize_rt_tasks() which needs to work under tasklist_lock and can't therefore grab cpuset_rwsem. We are fine with this, as this function is only called by sysrq and, if that gets triggered, DEADLINE guarantees are already gone out of the window anyway. Signed-off-by: Juri Lelli --- v8 -> v9: - Add comment in changelog regarding normalize_rt_tasks() (Peter) --- include/linux/cpuset.h | 5 +++++ kernel/cgroup/cpuset.c | 11 +++++++++++ kernel/sched/core.c | 33 ++++++++++++++++++++++++++------- 3 files changed, 42 insertions(+), 7 deletions(-) diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h index 7f1478c26a33..04c20de66afc 100644 --- a/include/linux/cpuset.h +++ b/include/linux/cpuset.h @@ -55,6 +55,8 @@ extern void cpuset_init_smp(void); extern void cpuset_force_rebuild(void); extern void cpuset_update_active_cpus(void); extern void cpuset_wait_for_hotplug(void); +extern void cpuset_read_lock(void); +extern void cpuset_read_unlock(void); extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask); extern void cpuset_cpus_allowed_fallback(struct task_struct *p); extern nodemask_t cpuset_mems_allowed(struct task_struct *p); @@ -176,6 +178,9 @@ static inline void cpuset_update_active_cpus(void) static inline void cpuset_wait_for_hotplug(void) { } +static inline void cpuset_read_lock(void) { } +static inline void cpuset_read_unlock(void) { } + static inline void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask) { diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 93414ea63252..d16e160a3b35 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -334,6 +334,17 @@ static struct cpuset top_cpuset = { */ DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem); + +void cpuset_read_lock(void) +{ + percpu_down_read(&cpuset_rwsem); +} + +void cpuset_read_unlock(void) +{ + percpu_up_read(&cpuset_rwsem); +} + static DEFINE_SPINLOCK(callback_lock); static struct workqueue_struct *cpuset_migrate_mm_wq; diff --git a/kernel/sched/core.c b/kernel/sched/core.c index acd6a9fe85bc..18e151c6b48d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4208,6 +4208,9 @@ static int __sched_setscheduler(struct task_struct *p, return retval; } + if (pi) + cpuset_read_lock(); + /* * Make sure no PI-waiters arrive (or leave) while we are * changing the priority of the task: @@ -4280,6 +4283,8 @@ static int __sched_setscheduler(struct task_struct *p, if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) { policy = oldpolicy = -1; task_rq_unlock(rq, p, &rf); + if (pi) + cpuset_read_unlock(); goto recheck; } @@ -4338,8 +4343,10 @@ static int __sched_setscheduler(struct task_struct *p, preempt_disable(); task_rq_unlock(rq, p, &rf); - if (pi) + if (pi) { + cpuset_read_unlock(); rt_mutex_adjust_pi(p); + } /* Run balance callbacks after we've adjusted the PI chain: */ balance_callback(rq); @@ -4349,6 +4356,8 @@ static int __sched_setscheduler(struct task_struct *p, unlock: task_rq_unlock(rq, p, &rf); + if (pi) + cpuset_read_unlock(); return retval; } @@ -4433,10 +4442,15 @@ do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param) rcu_read_lock(); retval = -ESRCH; p = find_process_by_pid(pid); - if (p != NULL) - retval = sched_setscheduler(p, policy, &lparam); + if (!p) { + rcu_read_unlock(); + goto exit; + } + get_task_struct(p); rcu_read_unlock(); - + retval = sched_setscheduler(p, policy, &lparam); + put_task_struct(p); +exit: return retval; } @@ -4564,10 +4578,15 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr, rcu_read_lock(); retval = -ESRCH; p = find_process_by_pid(pid); - if (p != NULL) - retval = sched_setattr(p, &attr); + if (!p) { + rcu_read_unlock(); + goto exit; + } + get_task_struct(p); rcu_read_unlock(); - + retval = sched_setattr(p, &attr); + put_task_struct(p); +exit: return retval; } -- 2.17.2