From patchwork Fri Jan 24 11:09:58 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Crystal Wood X-Patchwork-Id: 213248 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=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 30B34C32771 for ; Fri, 24 Jan 2020 11:10:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 071D524682 for ; Fri, 24 Jan 2020 11:10:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hGKBOwvY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387533AbgAXLKH (ORCPT ); Fri, 24 Jan 2020 06:10:07 -0500 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:45109 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2389813AbgAXLKF (ORCPT ); Fri, 24 Jan 2020 06:10:05 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579864204; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc; bh=K3NBi6Sf5iK2lQ6XY2SqwGkLxd++w8nf2TJFIHAXCmc=; b=hGKBOwvYEEClCbhvS+zbwqTZUuc736K2vRUguzwNgiH4nrwK2K92EXHzKZeQHwlTd5so0l Ixj1fa23qgjQI2AtMFMLaygWwgjM8QZz9X8S9hd77kYeRz3W/WzrXVIk/jeUTLZL06Besj GBg+CzGS8J9rzECJ/wAAjUu3TC2wm4w= 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-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@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: