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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 B45F3C43460 for ; Mon, 10 May 2021 15:11:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 94B90610A7 for ; Mon, 10 May 2021 15:11:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234727AbhEJPMx (ORCPT ); Mon, 10 May 2021 11:12:53 -0400 Received: from foss.arm.com ([217.140.110.172]:60728 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235938AbhEJPMY (ORCPT ); Mon, 10 May 2021 11:12:24 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2886B1692; Mon, 10 May 2021 08:11:19 -0700 (PDT) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 2115F3F719; Mon, 10 May 2021 08:11:18 -0700 (PDT) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de, bristot@redhat.com, yejune.deng@gmail.com Subject: [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread Date: Mon, 10 May 2021 16:10:23 +0100 Message-Id: <20210510151024.2448573-2-valentin.schneider@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210510151024.2448573-1-valentin.schneider@arm.com> References: <20210510151024.2448573-1-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org For all intents and purposes, the idle task is a per-CPU kthread. It isn't created via the same route as other pcpu kthreads however, and as a result it is missing a few bells and whistles: it fails kthread_is_per_cpu() and it doesn't have PF_NO_SETAFFINITY set. Fix the former by giving the idle task a kthread struct along with the KTHREAD_IS_PER_CPU flag. This requires some extra iffery as init_idle() call be called more than once on the same idle task. Signed-off-by: Valentin Schneider --- include/linux/kthread.h | 2 ++ kernel/kthread.c | 30 ++++++++++++++++++------------ kernel/sched/core.c | 21 +++++++++++++++------ 3 files changed, 35 insertions(+), 18 deletions(-) diff --git a/include/linux/kthread.h b/include/linux/kthread.h index 2484ed97e72f..d9133d6db308 100644 --- a/include/linux/kthread.h +++ b/include/linux/kthread.h @@ -33,6 +33,8 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data), unsigned int cpu, const char *namefmt); +void set_kthread_struct(struct task_struct *p); + void kthread_set_per_cpu(struct task_struct *k, int cpu); bool kthread_is_per_cpu(struct task_struct *k); diff --git a/kernel/kthread.c b/kernel/kthread.c index 6d3c488a0f82..77dd0ea1d35d 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -68,16 +68,6 @@ enum KTHREAD_BITS { KTHREAD_SHOULD_PARK, }; -static inline void set_kthread_struct(void *kthread) -{ - /* - * We abuse ->set_child_tid to avoid the new member and because it - * can't be wrongly copied by copy_process(). We also rely on fact - * that the caller can't exec, so PF_KTHREAD can't be cleared. - */ - current->set_child_tid = (__force void __user *)kthread; -} - static inline struct kthread *to_kthread(struct task_struct *k) { WARN_ON(!(k->flags & PF_KTHREAD)); @@ -103,6 +93,22 @@ static inline struct kthread *__to_kthread(struct task_struct *p) return kthread; } +void set_kthread_struct(struct task_struct *p) +{ + struct kthread *kthread; + + if (__to_kthread(p)) + return; + + kthread = kzalloc(sizeof(*kthread), GFP_KERNEL); + /* + * We abuse ->set_child_tid to avoid the new member and because it + * can't be wrongly copied by copy_process(). We also rely on fact + * that the caller can't exec, so PF_KTHREAD can't be cleared. + */ + p->set_child_tid = (__force void __user *)kthread; +} + void free_kthread_struct(struct task_struct *k) { struct kthread *kthread; @@ -272,8 +278,8 @@ static int kthread(void *_create) struct kthread *self; int ret; - self = kzalloc(sizeof(*self), GFP_KERNEL); - set_kthread_struct(self); + set_kthread_struct(current); + self = to_kthread(current); /* If user was SIGKILLed, I release the structure. */ done = xchg(&create->done, NULL); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 4a0668acd876..5bb720829d93 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7440,12 +7440,25 @@ void init_idle(struct task_struct *idle, int cpu) __sched_fork(0, idle); + /* + * The idle task doesn't need the kthread struct to function, but it + * is dressed up as a per-CPU kthread and thus needs to play the part + * if we want to avoid special-casing it in code that deals with per-CPU + * kthreads. + */ + set_kthread_struct(idle); + raw_spin_lock_irqsave(&idle->pi_lock, flags); raw_spin_lock(&rq->lock); idle->state = TASK_RUNNING; idle->se.exec_start = sched_clock(); - idle->flags |= PF_IDLE; + /* + * PF_KTHREAD should already be set at this point; regardless, make it + * look like a proper per-CPU kthread. + */ + idle->flags |= PF_IDLE | PF_KTHREAD | PF_NO_SETAFFINITY; + kthread_set_per_cpu(idle, cpu); scs_task_reset(idle); kasan_unpoison_task_stack(idle); @@ -7662,12 +7675,8 @@ static void balance_push(struct rq *rq) /* * Both the cpu-hotplug and stop task are in this case and are * required to complete the hotplug process. - * - * XXX: the idle task does not match kthread_is_per_cpu() due to - * histerical raisins. */ - if (rq->idle == push_task || - kthread_is_per_cpu(push_task) || + if (kthread_is_per_cpu(push_task) || is_migration_disabled(push_task)) { /* -- 2.25.1