From nobody Mon Sep 15 11:28:17 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 D99A6C54EBC for ; Thu, 12 Jan 2023 16:20:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232316AbjALQT7 (ORCPT ); Thu, 12 Jan 2023 11:19:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53506 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237148AbjALQSo (ORCPT ); Thu, 12 Jan 2023 11:18:44 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA78F1DF33 for ; Thu, 12 Jan 2023 08:14:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1673540089; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=w00boU31zsjQBa+3K2UDs+4jXA9UVArYHCfP1r7mcI8=; b=DwZijw/CINRwkXzHndzKoYbndOm36K/cqF6CDrpJoUc88XIPVe2QoHYNmgJF/R9C9O5xhx RiKW6rgz4uBT6uFKYg0J5yOcnqU3hmnNYg3fJkz2HjF7FPlBLKdL+039xmS0xxFTxRcpkN u2TQhZWsx1IzEzfa8Q9JNI9QSKnGxLs= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-319-EI-iwW-NOU-Eb7GKjDJBEA-1; Thu, 12 Jan 2023 11:14:45 -0500 X-MC-Unique: EI-iwW-NOU-Eb7GKjDJBEA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 031423C0E201; Thu, 12 Jan 2023 16:14:44 +0000 (UTC) Received: from vschneid.remote.csb (unknown [10.33.36.188]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 071402166B26; Thu, 12 Jan 2023 16:14:42 +0000 (UTC) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: Tejun Heo , Lai Jiangshan , Peter Zijlstra , Frederic Weisbecker , Juri Lelli , Phil Auld , Marcelo Tosatti Subject: [PATCH v8 5/5] workqueue: Unbind kworkers before sending them to exit() Date: Thu, 12 Jan 2023 16:14:31 +0000 Message-Id: <20230112161431.860196-6-vschneid@redhat.com> In-Reply-To: <20230112161431.860196-1-vschneid@redhat.com> References: <20230112161431.860196-1-vschneid@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" It has been reported that isolated CPUs can suffer from interference due to per-CPU kworkers waking up just to die. A surge of workqueue activity during initial setup of a latency-sensitive application (refresh_vm_stats() being one of the culprits) can cause extra per-CPU kworkers to be spawned. Then, said latency-sensitive task can be running merrily on an isolated CPU only to be interrupted sometime later by a kworker marked for death (cf. IDLE_WORKER_TIMEOUT, 5 minutes after last kworker activity). Prevent this by affining kworkers to the wq_unbound_cpumask (which doesn't contain isolated CPUs, cf. HK_TYPE_WQ) before waking them up after marking them with WORKER_DIE. Changing the affinity does require a sleepable context, leverage the newly introduced pool->idle_cull_work to get that. Remove dying workers from pool->workers and keep track of them in a separate list. This intentionally prevents for_each_loop_worker() from iterating over workers that are marked for death. Rename destroy_worker() to set_working_dying() to better reflect its effects and relationship with wake_dying_workers(). Signed-off-by: Valentin Schneider --- kernel/workqueue.c | 72 ++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 60 insertions(+), 12 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 8ece9bfa04a09..66e9baea48002 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -179,6 +179,7 @@ struct worker_pool { =20 struct worker *manager; /* L: purely informational */ struct list_head workers; /* A: attached workers */ + struct list_head dying_workers; /* A: workers about to die */ struct completion *detach_completion; /* all workers detached */ =20 struct ida worker_ida; /* worker IDs for task name */ @@ -1902,7 +1903,7 @@ static void worker_detach_from_pool(struct worker *wo= rker) list_del(&worker->node); worker->pool =3D NULL; =20 - if (list_empty(&pool->workers)) + if (list_empty(&pool->workers) && list_empty(&pool->dying_workers)) detach_completion =3D pool->detach_completion; mutex_unlock(&wq_pool_attach_mutex); =20 @@ -1991,21 +1992,44 @@ static void rebind_worker(struct worker *worker, st= ruct worker_pool *pool) WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask) < 0= ); } =20 +static void wake_dying_workers(struct list_head *cull_list) +{ + struct worker *worker, *tmp; + + list_for_each_entry_safe(worker, tmp, cull_list, entry) { + list_del_init(&worker->entry); + unbind_worker(worker); + /* + * If the worker was somehow already running, then it had to be + * in pool->idle_list when set_worker_dying() happened or we + * wouldn't have gotten here. + * + * Thus, the worker must either have observed the WORKER_DIE + * flag, or have set its state to TASK_IDLE. Either way, the + * below will be observed by the worker and is safe to do + * outside of pool->lock. + */ + wake_up_process(worker->task); + } +} + /** - * destroy_worker - destroy a workqueue worker + * set_worker_dying - Tag a worker for destruction * @worker: worker to be destroyed + * @list: transfer worker away from its pool->idle_list and into list * - * Destroy @worker and adjust @pool stats accordingly. The worker should - * be idle. + * Tag @worker for destruction and adjust @pool stats accordingly. The wo= rker + * should be idle. * * CONTEXT: * raw_spin_lock_irq(pool->lock). */ -static void destroy_worker(struct worker *worker) +static void set_worker_dying(struct worker *worker, struct list_head *list) { struct worker_pool *pool =3D worker->pool; =20 lockdep_assert_held(&pool->lock); + lockdep_assert_held(&wq_pool_attach_mutex); =20 /* sanity check frenzy */ if (WARN_ON(worker->current_work) || @@ -2016,9 +2040,10 @@ static void destroy_worker(struct worker *worker) pool->nr_workers--; pool->nr_idle--; =20 - list_del_init(&worker->entry); worker->flags |=3D WORKER_DIE; - wake_up_process(worker->task); + + list_move(&worker->entry, list); + list_move(&worker->node, &pool->dying_workers); } =20 /** @@ -2065,11 +2090,24 @@ static void idle_worker_timeout(struct timer_list *= t) * * This goes through a pool's idle workers and gets rid of those that have= been * idle for at least IDLE_WORKER_TIMEOUT seconds. + * + * We don't want to disturb isolated CPUs because of a pcpu kworker being + * culled, so this also resets worker affinity. This requires a sleepable + * context, hence the split between timer callback and work item. */ static void idle_cull_fn(struct work_struct *work) { struct worker_pool *pool =3D container_of(work, struct worker_pool, idle_= cull_work); + struct list_head cull_list; =20 + INIT_LIST_HEAD(&cull_list); + /* + * Grabbing wq_pool_attach_mutex here ensures an already-running worker + * cannot proceed beyong worker_detach_from_pool() in its self-destruct + * path. This is required as a previously-preempted worker could run after + * set_worker_dying() has happened but before wake_dying_workers() did. + */ + mutex_lock(&wq_pool_attach_mutex); raw_spin_lock_irq(&pool->lock); =20 while (too_many_workers(pool)) { @@ -2084,10 +2122,12 @@ static void idle_cull_fn(struct work_struct *work) break; } =20 - destroy_worker(worker); + set_worker_dying(worker, &cull_list); } =20 raw_spin_unlock_irq(&pool->lock); + wake_dying_workers(&cull_list); + mutex_unlock(&wq_pool_attach_mutex); } =20 static void send_mayday(struct work_struct *work) @@ -2451,12 +2491,12 @@ static int worker_thread(void *__worker) /* am I supposed to die? */ if (unlikely(worker->flags & WORKER_DIE)) { raw_spin_unlock_irq(&pool->lock); - WARN_ON_ONCE(!list_empty(&worker->entry)); set_pf_worker(false); =20 set_task_comm(worker->task, "kworker/dying"); ida_free(&pool->worker_ida, worker->id); worker_detach_from_pool(worker); + WARN_ON_ONCE(!list_empty(&worker->entry)); kfree(worker); return 0; } @@ -3530,6 +3570,7 @@ static int init_worker_pool(struct worker_pool *pool) timer_setup(&pool->mayday_timer, pool_mayday_timeout, 0); =20 INIT_LIST_HEAD(&pool->workers); + INIT_LIST_HEAD(&pool->dying_workers); =20 ida_init(&pool->worker_ida); INIT_HLIST_NODE(&pool->hash_node); @@ -3618,8 +3659,11 @@ static void rcu_free_pool(struct rcu_head *rcu) static void put_unbound_pool(struct worker_pool *pool) { DECLARE_COMPLETION_ONSTACK(detach_completion); + struct list_head cull_list; struct worker *worker; =20 + INIT_LIST_HEAD(&cull_list); + lockdep_assert_held(&wq_pool_mutex); =20 if (--pool->refcnt) @@ -3652,21 +3696,25 @@ static void put_unbound_pool(struct worker_pool *po= ol) rcuwait_wait_event(&manager_wait, !(pool->flags & POOL_MANAGER_ACTIVE), TASK_UNINTERRUPTIBLE); + + mutex_lock(&wq_pool_attach_mutex); raw_spin_lock_irq(&pool->lock); if (!(pool->flags & POOL_MANAGER_ACTIVE)) { pool->flags |=3D POOL_MANAGER_ACTIVE; break; } raw_spin_unlock_irq(&pool->lock); + mutex_unlock(&wq_pool_attach_mutex); } =20 while ((worker =3D first_idle_worker(pool))) - destroy_worker(worker); + set_worker_dying(worker, &cull_list); WARN_ON(pool->nr_workers || pool->nr_idle); raw_spin_unlock_irq(&pool->lock); =20 - mutex_lock(&wq_pool_attach_mutex); - if (!list_empty(&pool->workers)) + wake_dying_workers(&cull_list); + + if (!list_empty(&pool->workers) || !list_empty(&pool->dying_workers)) pool->detach_completion =3D &detach_completion; mutex_unlock(&wq_pool_attach_mutex); =20 --=20 2.31.1