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 E6A99C433F5 for ; Tue, 4 Oct 2022 16:47:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230008AbiJDQrd (ORCPT ); Tue, 4 Oct 2022 12:47:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46040 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229719AbiJDQrb (ORCPT ); Tue, 4 Oct 2022 12:47:31 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E359B20BFB; Tue, 4 Oct 2022 09:47:29 -0700 (PDT) Date: Tue, 4 Oct 2022 18:47:26 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1664902047; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=xFLeaZNysEsn0UTLLCGuw736dT8SNd3jnhai8kQD4aE=; b=Csnvsvllv7H1sbQ5v8vMk+zY8ETUd8TKZyb8EKMnpm66M8N8B+xzsia/cuZFs84maqZtL+ t6qH8RBzGQHZdlJdxzhfJSI0V6BRYuuekdTpEAPBsCFRvLg6MHeMMUF3P3lCh4nlOiyv78 vZmEHTimmfLGf71VrcvTP3i1QyVUapY7a362CUMnvbAzQ3G+K8AQJdGlpD6mjapYIgxeT1 OsQUVbgeVPOWa9mJYcuksC3LCqcaKSFVKqrVz7OoQhN/muFrKgf3J/JElL/Y9QxintMMJt dkDGcJSQUQRw/RYsYrJj+ZYGo61Lg53or7m9Yu4M0nkGogJZEabZm1HKsVG1oQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1664902047; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=xFLeaZNysEsn0UTLLCGuw736dT8SNd3jnhai8kQD4aE=; b=7sjin08RaVatGszkKF7K7EMZAssiNXhWJvulNA2+NdiUDK0ahBM5jQeIHdXjpfgBMxA1CF 9c4PWtiOcOOC4oCA== From: Sebastian Andrzej Siewior To: Zqiang Cc: tglx@linutronix.de, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, Peter Zijlstra Subject: Re: [PATCH] irq_work: Migrate the remaining work of the offline CPU on PREEMPT_RT Message-ID: References: <20220925104111.1454100-1-qiang1.zhang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20220925104111.1454100-1-qiang1.zhang@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022-09-25 18:41:11 [+0800], Zqiang wrote: > When CPU goes offline and invoke CPU_DYING callbacks, the > smpcfd_dying_cpu() be invoked to flush the remaining irq_work of the > offline CPU, for lazy irq_work, will wakeup per-CPU irq_work kthreads > to invoke callbacks, but the irq_work kthreads are in TASK_PARKED > state, will not get the actual wakeup, resulting in the remaining lazy > irq_work not being executed. > > This commit requeue remaining of lazy irq_work to online CPU. At CPU_DYING the CPU runs with disabled interrupts so we can't invoke the remaining callbacks directly. Migrating them to another CPU will solve the problem but callbacks enqueued with irq_work_queue_on() will then be invoked on the wrong CPU. Is there a specific irq_work item that made you aware of this? > Signed-off-by: Zqiang > --- > include/linux/irq_work.h | 1 + > kernel/cpu.c | 1 + > kernel/irq_work.c | 20 ++++++++++++++++++++ > 3 files changed, 22 insertions(+) > > diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h > index 8cd11a223260..900d9053a62d 100644 > --- a/include/linux/irq_work.h > +++ b/include/linux/irq_work.h > @@ -66,6 +66,7 @@ void irq_work_sync(struct irq_work *work); > void irq_work_run(void); > bool irq_work_needs_cpu(void); > void irq_work_single(void *arg); > +void irq_work_migrate(int cpu); > #else > static inline bool irq_work_needs_cpu(void) { return false; } > static inline void irq_work_run(void) { } > diff --git a/kernel/cpu.c b/kernel/cpu.c > index bbad5e375d3b..70461b6d785d 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -1075,6 +1075,7 @@ static int takedown_cpu(unsigned int cpu) > > tick_cleanup_dead_cpu(cpu); > rcutree_migrate_callbacks(cpu); > + irq_work_migrate(cpu); > return 0; > } > > diff --git a/kernel/irq_work.c b/kernel/irq_work.c > index 7afa40fe5cc4..bfa21468c2df 100644 > --- a/kernel/irq_work.c > +++ b/kernel/irq_work.c > @@ -242,6 +242,26 @@ static void irq_work_run_list(struct llist_head *list) > irq_work_single(work); > } > > +void irq_work_migrate(int cpu) > +{ > + struct irq_work *work, *tmp; > + struct llist_node *llnode; > + struct llist_head *list = per_cpu_ptr(&lazy_list, cpu); > + > + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) > + return; > + > + if (llist_empty(list)) > + return; > + > + llnode = llist_del_all(list); > + llist_for_each_entry_safe(work, tmp, llnode, node.llist) { > + atomic_set(&work->node.a_flags, 0); > + irq_work_queue(work); > + } > +} > +EXPORT_SYMBOL_GPL(irq_work_migrate); > + > /* > * hotplug calls this through: > * hotplug_cfd() -> flush_smp_call_function_queue() > -- > 2.25.1 Sebastian