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=-6.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 8C08AC2D0DB for ; Fri, 24 Jan 2020 11:10:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5FFC12075D for ; Fri, 24 Jan 2020 11:10:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="TOVb3qFW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387592AbgAXLKM (ORCPT ); Fri, 24 Jan 2020 06:10:12 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:22166 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1731494AbgAXLKG (ORCPT ); Fri, 24 Jan 2020 06:10:06 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579864205; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc; bh=K3NBi6Sf5iK2lQ6XY2SqwGkLxd++w8nf2TJFIHAXCmc=; b=TOVb3qFW03Z/V2wVqevx61AOe5//RWwCoENSHfssSXHyiO4mKyddb0K/94y+ivi+ytporM 9t7cmQlj8XxwIIy9s3EBT8okn5P+DPIkfLpe7y10XQujJB5CMPMwvVIW3BXQ9CA2XVwKaY iWkK0GYxP9HLqPdGQABgYkW2cVtN7KE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-343-THEMo_z8NGO3QyxfJlrVUQ-1; Fri, 24 Jan 2020 06:10:02 -0500 X-MC-Unique: THEMo_z8NGO3QyxfJlrVUQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F32658017CC; Fri, 24 Jan 2020 11:10:00 +0000 (UTC) Received: from intel-purley-fpgabmp-02.ml3.eng.bos.redhat.com (intel-purley-fpgabmp-02.ml3.eng.bos.redhat.com [10.19.176.206]) by smtp.corp.redhat.com (Postfix) with ESMTP id 352A219C69; Fri, 24 Jan 2020 11:10:00 +0000 (UTC) From: Scott Wood To: Sebastian Andrzej Siewior Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt , Thomas Gleixner , Scott Wood Subject: [PATCH 1/2] sched: migrate_enable: Use per-cpu cpu_stop_work Date: Fri, 24 Jan 2020 06:09:58 -0500 Message-Id: <1579864199-13036-1-git-send-email-swood@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit e6c287b1512d ("sched: migrate_enable: Use stop_one_cpu_nowait()") adds a busy wait to deal with an edge case where the migrated thread can resume running on another CPU before the stopper has consumed cpu_stop_work. However, this is done with preemption disabled and can potentially lead to deadlock. While it is not guaranteed that the cpu_stop_work will be consumed before the migrating thread resumes and exits the stack frame, it is guaranteed that nothing other than the stopper can run on the old cpu between the migrating thread scheduling out and the cpu_stop_work being consumed. Thus, we can store cpu_stop_work in per-cpu data without it being reused too early. Fixes: e6c287b1512d ("sched: migrate_enable: Use stop_one_cpu_nowait()") Suggested-by: Sebastian Andrzej Siewior Signed-off-by: Scott Wood --- kernel/sched/core.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 754f6afb438d..7713e9c34ad1 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -8189,6 +8189,9 @@ static void migrate_disabled_sched(struct task_struct *p) p->migrate_disable_scheduled = 1; } +static DEFINE_PER_CPU(struct cpu_stop_work, migrate_work); +static DEFINE_PER_CPU(struct migration_arg, migrate_arg); + void migrate_enable(void) { struct task_struct *p = current; @@ -8227,22 +8230,25 @@ void migrate_enable(void) WARN_ON(smp_processor_id() != cpu); if (!is_cpu_allowed(p, cpu)) { - struct migration_arg arg = { .task = p }; - struct cpu_stop_work work; + struct migration_arg __percpu *arg; + struct cpu_stop_work __percpu *work; struct rq_flags rf; + work = this_cpu_ptr(&migrate_work); + arg = this_cpu_ptr(&migrate_arg); + WARN_ON_ONCE(!arg->done && !work->disabled && work->arg); + + arg->task = p; + arg->done = false; + rq = task_rq_lock(p, &rf); update_rq_clock(rq); - arg.dest_cpu = select_fallback_rq(cpu, p); + arg->dest_cpu = select_fallback_rq(cpu, p); task_rq_unlock(rq, p, &rf); stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop, - &arg, &work); + arg, work); __schedule(true); - if (!work.disabled) { - while (!arg.done) - cpu_relax(); - } } out: -- 1.8.3.1