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 34819C433F5 for ; Thu, 31 Mar 2022 13:21:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236768AbiCaNW6 (ORCPT ); Thu, 31 Mar 2022 09:22:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51358 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232629AbiCaNW5 (ORCPT ); Thu, 31 Mar 2022 09:22:57 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 6E8B21DEAB3 for ; Thu, 31 Mar 2022 06:21:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1648732869; 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=u+w6PvnKvqRPLK7dP9n2WRW7fwC2UrijjnF9LxNx4Mc=; b=c5bKxGxgHHESKIcBnYKN23TiPlBA7ae7SUNmQ+XTrMT7ziM7oklRfRpD8peXSL9CTUbP7w l64/rKtsLqyu6/hTq5jsH+5kF7JwOGx+K+Ip0bxzAdJWZq6ijtrSHU5y61qAoOy7O9YFPb G7xj05OAjzce5oNf1obfDGsl1yIQoSY= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-557-US1-0cXaN8qssD-_WsKH5g-1; Thu, 31 Mar 2022 09:21:06 -0400 X-MC-Unique: US1-0cXaN8qssD-_WsKH5g-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 78AE13822202; Thu, 31 Mar 2022 13:21:05 +0000 (UTC) Received: from pauld.bos.csb (dhcp-17-51.bos.redhat.com [10.18.17.51]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 45E42401E2A; Thu, 31 Mar 2022 13:21:05 +0000 (UTC) Date: Thu, 31 Mar 2022 09:21:04 -0400 From: Phil Auld To: Dietmar Eggemann Cc: linux-kernel@vger.kernel.org, Catalin Marinas , Will Deacon , Mark Rutland , Peter Zijlstra , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2] arch/arm64: Fix topology initialization for core scheduling Message-ID: <20220331132103.GB17613@pauld.bos.csb> References: <20220330155611.30216-1-pauld@redhat.com> <66f29bee-e26c-b40e-c3af-79d5297565d8@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <66f29bee-e26c-b40e-c3af-79d5297565d8@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 31, 2022 at 11:04:31AM +0200 Dietmar Eggemann wrote: > On 30/03/2022 17:56, Phil Auld wrote: > > Arm64 systems rely on store_cpu_topology() to call update_siblings_masks() > > to transfer the toplogy to the various cpu masks. This needs to be done > > before the call to notify_cpu_starting() which tells the scheduler about > > each cpu found, otherwise the core scheduling data structures are setup > > in a way that does not match the actual topology. > > > > Without this change stress-ng (which enables core scheduling in its prctl > > tests) causes a warning and then a crash (trimmed for legibility): > > > > [ 1853.805168] ------------[ cut here ]------------ > > [ 1853.809784] task_rq(b)->core != rq->core > > [ 1853.809792] WARNING: CPU: 117 PID: 0 at kernel/sched/fair.c:11102 cfs_prio_less+0x1b4/0x1c4 > > ... > > [ 1854.015210] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010 > > ... > > [ 1854.231256] Call trace: > > [ 1854.233689] pick_next_task+0x3dc/0x81c > > [ 1854.237512] __schedule+0x10c/0x4cc > > [ 1854.240988] schedule_idle+0x34/0x54 > > > > Fixes: 9edeaea1bc45 ("sched: Core-wide rq->lock") > > Signed-off-by: Phil Auld > > --- > > This is a similar issue to > > f2703def339c ("MIPS: smp: fill in sibling and core maps earlier") > > which fixed it for MIPS. > > > > v2: Fixed the commit message. No code change. > > Ah, the reason is that smt_mask is not correctly setup, so we bail on > `cpumask_weight(smt_mask) == 1` for !leaders in: > > notify_cpu_starting() > cpuhp_invoke_callback_range() > sched_cpu_starting() > sched_core_cpu_starting() > > which leads to rq->core not being correctly set for !leader-rq's. > Exactly, sorry I was not clearer. smt_mask must be setup correctly by the time sched_core_cpu_starting() is called. (Maybe I should crib some of the above lines into the commit message?) > LGTM. Tested on: HPE Apollo 70 X1 > > Reviewed-by: Dietmar Eggemann > Tested-by: Dietmar Eggemann > Thanks! Cheers, Phil > [...] > --