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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 095ADC00140 for ; Tue, 2 Aug 2022 08:42:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235493AbiHBImf (ORCPT ); Tue, 2 Aug 2022 04:42:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43644 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235746AbiHBIm1 (ORCPT ); Tue, 2 Aug 2022 04:42:27 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 806611834B for ; Tue, 2 Aug 2022 01:42:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659429745; 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=aT7p3QkgEShXnfExV1EoIhnpwMw5uLCIByiCReTweps=; b=Uz0Gu+Nu8OyIyPKqfoE4sagP+HfkdWMtN9HUeK9azieXAbAJy/1Hmy0OGj3Cs/J8aGZRtj RW3eEUa1c/XnN9zKo6gAj4bNPEKEwDx1q6Y4TtoaOBis2wTgTCwHI02YgqRomnp9HYM0F5 vFuAa6h72ttcj9eH/xgge2C2takEH1E= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-656-CedOCPNKMZK9aCdQ0qLD7Q-1; Tue, 02 Aug 2022 04:42:24 -0400 X-MC-Unique: CedOCPNKMZK9aCdQ0qLD7Q-1 Received: by mail-wr1-f71.google.com with SMTP id m7-20020adfa3c7000000b0021ef71807e3so3256596wrb.9 for ; Tue, 02 Aug 2022 01:42:24 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc; bh=aT7p3QkgEShXnfExV1EoIhnpwMw5uLCIByiCReTweps=; b=nSn/vYXF/tl5Dp7WPKGqGuq3h8ZA11IaWfdGW95iBca/f7dDQDQuoLD9wV14hG6SYe YMcxg+IXWfr5V+x6UOxY4PyuV4c4G8mqA4e/1MYfFjcwGYAhMV8MR15VQszte3Oew9tE Z8GJLbIHG1jn4Dk2QdCiuVsPBUkFGhEnEhwwN4PXMPqej7jUI1OAHBjhuiLVezm3sOuR q8PHKwY6Fnb3XXwV7sXMbifSK6AyCVD9FpQUp8TnPvqk1e/MK7OJBB5NJgwajNsEh3vW K31a0x1vQgbuRmSp3lvdivtPQ4jjYgHWFdlfvthMZ1f46oCHGlBv34cNdP9Dzt4aM6Y+ rapQ== X-Gm-Message-State: ACgBeo1bl8iSMSz5xHJ++exGStKJNbrhtCTPC4yArMUJeUb2CO9uKP1Z ifD+0I5D59xpdxPoZniRw8OHJYJnw9rRoxaSS7ZeJELxk+4nJ8LEcsTBC40g/rPhug6O0iEW9w+ RaBUg0yGzgwgm8RIUfIpq8OcXVgsHGP71NvtiGLfhekqbXdgRRhhQ74x/Fn7F7/ngHGPoyxitg4 FK X-Received: by 2002:a5d:64ac:0:b0:21d:7832:ecf9 with SMTP id m12-20020a5d64ac000000b0021d7832ecf9mr12430345wrp.86.1659429743139; Tue, 02 Aug 2022 01:42:23 -0700 (PDT) X-Google-Smtp-Source: AA6agR74cK2el17Wbd1YXJXEm2xi29pldGRwzrQiQ90NPJxxuSk4yZ7/hsHX7hk76lXVIbbV8g2m9g== X-Received: by 2002:a5d:64ac:0:b0:21d:7832:ecf9 with SMTP id m12-20020a5d64ac000000b0021d7832ecf9mr12430312wrp.86.1659429742675; Tue, 02 Aug 2022 01:42:22 -0700 (PDT) Received: from vschneid.remote.csb ([185.11.37.247]) by smtp.gmail.com with ESMTPSA id f12-20020a05600c154c00b003a31169a7f4sm24825800wmg.12.2022.08.02.01.42.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Aug 2022 01:42:22 -0700 (PDT) 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: [RFC PATCH v3 2/3] workqueue: Unbind workers before sending them to exit() Date: Tue, 2 Aug 2022 09:41:45 +0100 Message-Id: <20220802084146.3922640-3-vschneid@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20220802084146.3922640-1-vschneid@redhat.com> References: <20220802084146.3922640-1-vschneid@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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, so get rid of the pool->idle_timer and use a delayed_work instead. Ensure kworkers do not free their resources before the new kworker reaper has handled them by introducing a new struct worker.reaper field - this new field fills in a 4 byte hole in the second cacheline of struct worker. Signed-off-by: Valentin Schneider --- kernel/workqueue.c | 155 +++++++++++++++++++++++++++++------- kernel/workqueue_internal.h | 1 + 2 files changed, 126 insertions(+), 30 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 97cc41430a76..28cd58c684ee 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -167,9 +167,9 @@ struct worker_pool { int nr_workers; /* L: total number of workers */ int nr_idle; /* L: currently idle workers */ - struct list_head idle_list; /* L: list of idle workers */ - struct timer_list idle_timer; /* L: worker idle timeout */ - struct timer_list mayday_timer; /* L: SOS timer for workers */ + struct list_head idle_list; /* L: list of idle workers */ + struct delayed_work idle_reaper_work; /* L: worker idle timeout */ + struct timer_list mayday_timer; /* L: SOS timer for workers */ /* a workers is either on busy_hash or idle_list, or the manager */ DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER); @@ -1806,8 +1806,10 @@ static void worker_enter_idle(struct worker *worker) /* idle_list is LIFO */ list_add(&worker->entry, &pool->idle_list); - if (too_many_workers(pool) && !timer_pending(&pool->idle_timer)) - mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT); + if (too_many_workers(pool) && !delayed_work_pending(&pool->idle_reaper_work)) + mod_delayed_work(system_unbound_wq, + &pool->idle_reaper_work, + IDLE_WORKER_TIMEOUT); /* Sanity check nr_running. */ WARN_ON_ONCE(pool->nr_workers == pool->nr_idle && pool->nr_running); @@ -1972,9 +1974,72 @@ static struct worker *create_worker(struct worker_pool *pool) return NULL; } +static void unbind_worker(struct worker *worker) +{ + lockdep_assert_held(&wq_pool_mutex); + + kthread_set_per_cpu(worker->task, -1); + if (cpumask_intersects(wq_unbound_cpumask, cpu_active_mask)) + WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0); + else + WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0); +} + +static void rebind_worker(struct worker *worker, struct worker_pool *pool) +{ + kthread_set_per_cpu(worker->task, pool->cpu); + WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask) < 0); +} + +static void reap_workers(struct list_head *reaplist) +{ + struct worker *worker, *tmp; + + list_for_each_entry_safe(worker, tmp, reaplist, 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 destroy_worker() 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. + */ + WRITE_ONCE(worker->reaped, true); + wake_up_process(worker->task); + } +} + +/* + * Unlikely as it may be, a worker could wake after destroy_worker() has + * happened but before reap_workers(). WORKER_DIE would be set in worker->flags, + * so it would be able to kfree(worker) and head out to do_exit(). + * + * Rather than make the reaper wait for each to-be-reaped kworker to exit and + * kfree(worker) itself, make the kworkers (which have nothing to do but go + * do_exit() anyway) wait for the reaper to be done with them. + */ +static void worker_wait_reaped(struct worker *worker) +{ + WARN_ON_ONCE(current != worker->task); + + for (;;) { + set_current_state(TASK_INTERRUPTIBLE); + if (READ_ONCE(worker->reaped)) + break; + schedule(); + } + __set_current_state(TASK_RUNNING); +} + /** * destroy_worker - destroy a workqueue worker * @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. @@ -1982,7 +2047,7 @@ static struct worker *create_worker(struct worker_pool *pool) * CONTEXT: * raw_spin_lock_irq(pool->lock). */ -static void destroy_worker(struct worker *worker) +static void destroy_worker(struct worker *worker, struct list_head *list) { struct worker_pool *pool = worker->pool; @@ -1997,34 +2062,64 @@ static void destroy_worker(struct worker *worker) pool->nr_workers--; pool->nr_idle--; - list_del_init(&worker->entry); worker->flags |= WORKER_DIE; - wake_up_process(worker->task); + + list_move(&worker->entry, list); } -static void idle_worker_timeout(struct timer_list *t) +/** + * idle_reaper_fn - reap workers that have been idle for too long. + * + * Unbinding marked-for-destruction workers requires a sleepable context, as + * changing a task's affinity is not an atomic operation, and we don't want + * to disturb isolated CPUs IDLE_WORKER_TIMEOUT in the future just for a kworker + * to do_exit(). + * + * Percpu kworkers should meet the conditions for the affinity change to not + * block (not migration-disabled and not running), but there is no *hard* + * guarantee that they are not running when we get here. + * + * The delayed_work is only ever modified under raw_spin_lock_irq(pool->lock). + */ +static void idle_reaper_fn(struct work_struct *work) { - struct worker_pool *pool = from_timer(pool, t, idle_timer); + struct delayed_work *dwork = to_delayed_work(work); + struct worker_pool *pool = container_of(dwork, struct worker_pool, idle_reaper_work); + struct list_head reaplist; + struct worker *worker; + + INIT_LIST_HEAD(&reaplist); raw_spin_lock_irq(&pool->lock); while (too_many_workers(pool)) { - struct worker *worker; unsigned long expires; + unsigned long now = jiffies; /* idle_list is kept in LIFO order, check the last one */ worker = list_entry(pool->idle_list.prev, struct worker, entry); expires = worker->last_active + IDLE_WORKER_TIMEOUT; - if (time_before(jiffies, expires)) { - mod_timer(&pool->idle_timer, expires); + /* + * Careful: queueing a work item from here can and will cause a + * self-deadlock when dealing with an unbound pool. However, + * here the delay *cannot* be zero and *has* to be in the + * future, which works. + */ + if (time_before(now, expires)) { + mod_delayed_work(system_unbound_wq, + &pool->idle_reaper_work, + expires - now); break; } - destroy_worker(worker); + destroy_worker(worker, &reaplist); } - raw_spin_unlock_irq(&pool->lock); + + mutex_lock(&wq_pool_mutex); + reap_workers(&reaplist); + mutex_unlock(&wq_pool_mutex); } static void send_mayday(struct work_struct *work) @@ -2388,6 +2483,9 @@ static int worker_thread(void *__worker) /* am I supposed to die? */ if (unlikely(worker->flags & WORKER_DIE)) { raw_spin_unlock_irq(&pool->lock); + + worker_wait_reaped(worker); + WARN_ON_ONCE(!list_empty(&worker->entry)); set_pf_worker(false); @@ -3454,7 +3552,7 @@ static int init_worker_pool(struct worker_pool *pool) INIT_LIST_HEAD(&pool->idle_list); hash_init(pool->busy_hash); - timer_setup(&pool->idle_timer, idle_worker_timeout, TIMER_DEFERRABLE); + INIT_DEFERRABLE_WORK(&pool->idle_reaper_work, idle_reaper_fn); timer_setup(&pool->mayday_timer, pool_mayday_timeout, 0); @@ -3559,8 +3657,11 @@ static bool wq_manager_inactive(struct worker_pool *pool) static void put_unbound_pool(struct worker_pool *pool) { DECLARE_COMPLETION_ONSTACK(detach_completion); + struct list_head reaplist; struct worker *worker; + INIT_LIST_HEAD(&reaplist); + lockdep_assert_held(&wq_pool_mutex); if (--pool->refcnt) @@ -3588,10 +3689,12 @@ static void put_unbound_pool(struct worker_pool *pool) pool->flags |= POOL_MANAGER_ACTIVE; while ((worker = first_idle_worker(pool))) - destroy_worker(worker); + destroy_worker(worker, &reaplist); WARN_ON(pool->nr_workers || pool->nr_idle); raw_spin_unlock_irq(&pool->lock); + reap_workers(&reaplist); + mutex_lock(&wq_pool_attach_mutex); if (!list_empty(&pool->workers)) pool->detach_completion = &detach_completion; @@ -3601,7 +3704,7 @@ static void put_unbound_pool(struct worker_pool *pool) wait_for_completion(pool->detach_completion); /* shut down the timers */ - del_timer_sync(&pool->idle_timer); + cancel_delayed_work_sync(&pool->idle_reaper_work); del_timer_sync(&pool->mayday_timer); /* RCU protected to allow dereferences from get_work_pool() */ @@ -4999,13 +5102,8 @@ static void unbind_workers(int cpu) raw_spin_unlock_irq(&pool->lock); - for_each_pool_worker(worker, pool) { - kthread_set_per_cpu(worker->task, -1); - if (cpumask_intersects(wq_unbound_cpumask, cpu_active_mask)) - WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0); - else - WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0); - } + for_each_pool_worker(worker, pool) + unbind_worker(worker); mutex_unlock(&wq_pool_attach_mutex); } @@ -5030,11 +5128,8 @@ static void rebind_workers(struct worker_pool *pool) * of all workers first and then clear UNBOUND. As we're called * from CPU_ONLINE, the following shouldn't fail. */ - for_each_pool_worker(worker, pool) { - kthread_set_per_cpu(worker->task, pool->cpu); - WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, - pool->attrs->cpumask) < 0); - } + for_each_pool_worker(worker, pool) + rebind_worker(worker, pool); raw_spin_lock_irq(&pool->lock); diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h index e00b1204a8e9..a3d60e10a76f 100644 --- a/kernel/workqueue_internal.h +++ b/kernel/workqueue_internal.h @@ -46,6 +46,7 @@ struct worker { unsigned int flags; /* X: flags */ int id; /* I: worker id */ int sleeping; /* None */ + int reaped; /* None */ /* * Opaque string set with work_set_desc(). Printed out with task -- 2.31.1