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=-3.9 required=3.0 tests=BAYES_00,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 12BAAC433E7 for ; Fri, 9 Oct 2020 17:54:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 95AF822277 for ; Fri, 9 Oct 2020 17:54:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="c9dS7MKy" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388603AbgJIRyq (ORCPT ); Fri, 9 Oct 2020 13:54:46 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:53400 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731500AbgJIRyn (ORCPT ); Fri, 9 Oct 2020 13:54:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1602266082; 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=j5lS/XyFlFyWGw8WTiJQaNa1adNpHA0kZZEkG97cs5w=; b=c9dS7MKycG4EJVgiHH2hTDRuPg0zapEH4Ys5d64WmFiGE1ErkE+d1dSfRlQ8OMRcx53mXT /mYmjfZE0a55WTVGxVIMCg0F69kHK9L6uN26xTUOUg6Kruod20RWV8VrHc8nBhouftGzVD 9CSVHMQQOMArPB72tmAnSaw0jhGWrWQ= 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-108-GNB71R8cMd2BnObDobOm0g-1; Fri, 09 Oct 2020 13:54:38 -0400 X-MC-Unique: GNB71R8cMd2BnObDobOm0g-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 CD283108E1A0; Fri, 9 Oct 2020 17:54:36 +0000 (UTC) Received: from ovpn-66-175.rdu2.redhat.com (unknown [10.10.67.175]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2DA7119D7C; Fri, 9 Oct 2020 17:54:35 +0000 (UTC) Message-ID: <942e0ffb37a4580982206d72404c521d72d38314.camel@redhat.com> Subject: Re: [tip: locking/core] lockdep: Fix lockdep recursion From: Qian Cai To: Peter Zijlstra , "Paul E. McKenney" Cc: Steven Rostedt , Ingo Molnar , x86 , linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org, Linux Next Mailing List , Stephen Rothwell , Boqun Feng Date: Fri, 09 Oct 2020 13:54:34 -0400 In-Reply-To: References: <160223032121.7002.1269740091547117869.tip-bot2@tip-bot2> <20201009135837.GD29330@paulmck-ThinkPad-P72> <20201009162352.GR2611@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-next@vger.kernel.org On Fri, 2020-10-09 at 13:36 -0400, Qian Cai wrote: > Back to x86, we have: > > start_secondary() > smp_callin() > apic_ap_setup() > setup_local_APIC() > printk() in certain conditions. > > which is before smp_store_cpu_info(). > > Can't we add a rcu_cpu_starting() at the very top for each start_secondary(), > secondary_start_kernel(), smp_start_secondary() etc, so we don't worry about > any printk() later? This is rather irony. rcu_cpu_starting() is taking a lock and then reports itself. [ 8.826732][ T0] __lock_acquire.cold.76+0x2ad/0x3e0 [ 8.826732][ T0] lock_acquire+0x1c8/0x820 [ 8.826732][ T0] _raw_spin_lock_irqsave+0x30/0x50 [ 8.826732][ T0] rcu_cpu_starting+0xd0/0x2c0 [ 8.826732][ T0] start_secondary+0x10/0x2a0 [ 8.826732][ T0] secondary_startup_64_no_verify+0xb8/0xbb