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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, 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 7AB26C43387 for ; Thu, 17 Jan 2019 08:48:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4577D20856 for ; Thu, 17 Jan 2019 08:48:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730838AbfAQIsI (ORCPT ); Thu, 17 Jan 2019 03:48:08 -0500 Received: from mail-wm1-f68.google.com ([209.85.128.68]:33840 "EHLO mail-wm1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730777AbfAQIsC (ORCPT ); Thu, 17 Jan 2019 03:48:02 -0500 Received: by mail-wm1-f68.google.com with SMTP id y185so476008wmd.1 for ; Thu, 17 Jan 2019 00:48:00 -0800 (PST) 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=Xjjyx0Yjyd2PsWK9SkLNxWwUaL+ykG1i9L2fhMC829Y=; b=bTK04mHBdeHu694/s1C52GlmD/dWsshd4s4z/uLLHlk8Fdrq/ixJXEWHUk3cds9+XI E4j9NYEYny7LcjMuTUtHJuPOcN9TPlm5wi0IBoTCotqeCvMUCk1af69g3Uqif5aqyGpJ zv0927APQ9dBQhL6gNK98nM7KLMeVMqS1NSdGXbYaULcBB9wM05mNqHQHCfSMvl1A4GB 5skT6AryGaFqcZ4DWpngtPJ8Dgry4HQv3ak5Cc+ds2rJub/g9vAerk2l6AxAjHdusUnm R9aWj6GG8vzC+j6iOEP/JrvtbibSLPW90TLM1ySQgfrTavXvbaHCau/O3FeATvIIJpEw EnKA== X-Gm-Message-State: AJcUukcqBhas1aM2il1kbJWlh7RAa4WOS3Jon/PMG9RTjJr/BJwSMCxI ocBrJWNyEzeikfDvx9btRTU2Cg== X-Google-Smtp-Source: ALg8bN4CChnSHyfPY9CSJGlALe5DKWmpxe3eNxb7aLHUkZQBp/s+Wnz1CQHlrn1wiDB9t3p/VAnPQw== X-Received: by 2002:a1c:5f8a:: with SMTP id t132mr11105254wmb.40.1547714879728; Thu, 17 Jan 2019 00:47:59 -0800 (PST) Received: from localhost.localdomain.home ([151.15.254.62]) by smtp.gmail.com with ESMTPSA id 199sm41984992wmh.21.2019.01.17.00.47.58 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 17 Jan 2019 00:47:59 -0800 (PST) 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, cgroups@vger.kernel.org, Juri Lelli Subject: [PATCH v6 4/5] sched/core: Prevent race condition between cpuset and __sched_setscheduler() Date: Thu, 17 Jan 2019 09:47:38 +0100 Message-Id: <20190117084739.17078-5-juri.lelli@redhat.com> X-Mailer: git-send-email 2.17.2 In-Reply-To: <20190117084739.17078-1-juri.lelli@redhat.com> References: <20190117084739.17078-1-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 callback_lock from core scheduler, so to prevent situations such as the one described above from happening. Signed-off-by: Mathieu Poirier Signed-off-by: Juri Lelli --- v5->v6: Added more descriptive comments about why callback_lock gives the holder read-only access to cpusets. --- include/linux/cpuset.h | 6 ++++++ kernel/cgroup/cpuset.c | 25 ++++++++++++++++++++++++- kernel/sched/core.c | 10 ++++++++++ 3 files changed, 40 insertions(+), 1 deletion(-) diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h index 934633a05d20..8e5a8dd0622b 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_only_lock(void); +extern void cpuset_read_only_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 +178,10 @@ static inline void cpuset_update_active_cpus(void) static inline void cpuset_wait_for_hotplug(void) { } +static inline void cpuset_read_only_lock(void) { } + +static inline void cpuset_read_only_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 54b8ff5de7c8..8ee1b24b6353 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -330,7 +330,8 @@ static struct cpuset top_cpuset = { * __alloc_pages(). * * If a task is only holding callback_lock, then it has read-only - * access to cpusets. + * access to cpusets. Mind that callback_lock might be grabbed from other + * subsystems as well (via cpuset_read_only_lock()). * * Now, the task_struct fields mems_allowed and mempolicy may be changed * by other task, we use alloc_lock in the task_struct fields to protect @@ -3218,6 +3219,28 @@ void __init cpuset_init_smp(void) BUG_ON(!cpuset_migrate_mm_wq); } +/** + * cpuset_read_only_lock - Grab the callback_lock from cpuset subsystem. + * + * Description: As described in full details the comment above cpuset_mutex + * and callback_lock definitions, holding callback_lock gives the holder + * read-only access to cpusets. Even though it might look counter-intuitive + * (as callback_lock is a spinlock), in fact a task must hold both + * callback_lock _and_ cpuset_mutex to modify cpusets (write access). + */ +void cpuset_read_only_lock(void) +{ + raw_spin_lock(&callback_lock); +} + +/** + * cpuset_read_only_unlock - Release the callback_lock from cpuset subsystem. + */ +void cpuset_read_only_unlock(void) +{ + raw_spin_unlock(&callback_lock); +} + /** * cpuset_cpus_allowed - return cpus_allowed mask from a tasks cpuset. * @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed. diff --git a/kernel/sched/core.c b/kernel/sched/core.c index f5263383170e..d928a42b8852 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4224,6 +4224,13 @@ static int __sched_setscheduler(struct task_struct *p, rq = task_rq_lock(p, &rf); update_rq_clock(rq); + /* + * Make sure we don't race with the cpuset subsystem where root + * domains can be rebuilt or modified while operations like DL + * admission checks are carried out. + */ + cpuset_read_only_lock(); + /* * Changing the policy of the stop threads its a very bad idea: */ @@ -4285,6 +4292,7 @@ static int __sched_setscheduler(struct task_struct *p, /* Re-check policy now with rq lock held: */ if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) { policy = oldpolicy = -1; + cpuset_read_only_unlock(); task_rq_unlock(rq, p, &rf); goto recheck; } @@ -4342,6 +4350,7 @@ static int __sched_setscheduler(struct task_struct *p, /* Avoid rq from going away on us: */ preempt_disable(); + cpuset_read_only_unlock(); task_rq_unlock(rq, p, &rf); if (pi) @@ -4354,6 +4363,7 @@ static int __sched_setscheduler(struct task_struct *p, return 0; unlock: + cpuset_read_only_unlock(); task_rq_unlock(rq, p, &rf); return retval; } -- 2.17.2