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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 51B45C38BFF for ; Mon, 24 Feb 2020 22:16:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 206CB218AC for ; Mon, 24 Feb 2020 22:16:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Q6SIpBLM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728079AbgBXWQE (ORCPT ); Mon, 24 Feb 2020 17:16:04 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:54251 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726651AbgBXWQD (ORCPT ); Mon, 24 Feb 2020 17:16:03 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1582582562; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=DNSD66ImMoPsjxgik/kryHw2+qoaM+eMsRblP5sq1ko=; b=Q6SIpBLMhyaRHyfEj/r2uUb7ZLrmPCsvQA9MgfjwhFai7t22B+v8UR7rnCBmjJFivgJaI9 /mszhL+yNZi14GV0hFM5UtJ6wCXQT8Q4q3hn9X5s9IBCmD4zAmqHFLTFDL35rdEmCqRr/o jRWQHRPDLwgY5PhRPcZMb/tk0ttz1V0= 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-248-laDNQN88PKGHPbLLdvhBnQ-1; Mon, 24 Feb 2020 17:15:54 -0500 X-MC-Unique: laDNQN88PKGHPbLLdvhBnQ-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 6B14E100DFC7; Mon, 24 Feb 2020 22:15:52 +0000 (UTC) Received: from ovpn-118-56.phx2.redhat.com (ovpn-118-56.phx2.redhat.com [10.3.118.56]) by smtp.corp.redhat.com (Postfix) with ESMTP id B4687393; Mon, 24 Feb 2020 22:15:50 +0000 (UTC) Message-ID: <4f7ecfa4034463892e2d211d3cba2b9c8f6449c7.camel@redhat.com> Subject: Re: [PATCH RT 15/25] sched: migrate_enable: Use select_fallback_rq() From: Scott Wood To: Sebastian Andrzej Siewior , Tom Zanussi Cc: LKML , linux-rt-users , Steven Rostedt , Thomas Gleixner , Carsten Emde , John Kacur , Daniel Wagner Date: Mon, 24 Feb 2020 16:15:49 -0600 In-Reply-To: <20200224160529.f5lg44gyk2mgayd4@linutronix.de> References: <20200224094349.5x6dca4tggtmmbnq@linutronix.de> <1582558266.12738.32.camel@kernel.org> <20200224160529.f5lg44gyk2mgayd4@linutronix.de> Organization: Red Hat Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit 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 On Mon, 2020-02-24 at 17:05 +0100, Sebastian Andrzej Siewior wrote: > On 2020-02-24 09:31:06 [-0600], Tom Zanussi wrote: > > On Mon, 2020-02-24 at 10:43 +0100, Sebastian Andrzej Siewior wrote: > > > On 2020-02-21 15:24:43 [-0600], zanussi@kernel.org wrote: > > > > From: Scott Wood > > > > > > > > v4.14.170-rt75-rc1 stable review patch. > > > > If anyone has any objections, please let me know. > > > > > > This creates bug which is stuffed later via > > > sched: migrate_enable: Busy loop until the migration request is > > > completed > > > > > > So if apply this, please take the bug fix, too. This is Stevens queue > > > for reference: > > > > [PATCH RT 22/30] sched: migrate_enable: Use select_fallback_rq() > > > > > > ^^ bug introduced > > > > > > > Hmm, it seemed from the comment on the 4.19 series that it was '24/32 > > sched: migrate_enable: Use stop_one_cpu_nowait()' that required 'sched: > > migrate_enable: Busy loop until the migration request is > > completed' as a bug fix. > > > > > > https://lore.kernel.org/linux-rt-users/20200122083130.kuu3yppckhyjrr4u@linutronix.de/#t > > > > I didn't take the stop_one_cpu_nowait() one, so didn't take the busy > > loop one either. > > Ach, it was the different WARN_ON() then. So this might not introduce > any bug then. *Might*. > Steven backported the whole pile and you took just this one patch. The > whole set was tested in devel and uncovered a problem which was fixed > later. Taking only a part *may* expose other problems it *may* be fine. Taking up to this patch should be OK (well, you still have the current->state clobbering, but it shouldn't introduce any new known bugs). The busy loop patch itself has a followup fix though (in theory the busy loop could deadlock): 2dcd94b443c5dcbc ("sched: migrate_enable: Use per-cpu cpu_stop_work") which should be considered for v4.19 rt stable which has the busy loop patch. -Scott