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=-6.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, 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 22BDCC433E7 for ; Tue, 13 Oct 2020 10:34:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CC29720878 for ; Tue, 13 Oct 2020 10:34:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="TC9l4f3K" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388281AbgJMKeh (ORCPT ); Tue, 13 Oct 2020 06:34:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56238 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388136AbgJMKeg (ORCPT ); Tue, 13 Oct 2020 06:34:36 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 972CAC0613D0; Tue, 13 Oct 2020 03:34:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=f6v7bo6Fu/9tm/yz2e4NZSbO5J9cvh1XjyZdnBx9s/8=; b=TC9l4f3KVyc/dPz6Wnb3hCXWQl T1TlVcnSiIBy0avI94VPkr3yD9hjS2stmauhed17c7FTYnlR+TjsVhH6NqT5OC/QcEXNUy7QV+r0b kFHnQ0Ab9TbUTOsS2bCMdupGIXIQ+UUBmZJMAKr+w2NA+VrEW2bOtXZBWXTAHgVgTe/PQVjYoLEPO EBxTk4+ZBw5OqXYWsZEDfz0JpfIcDa6DCILhfFlerF4Kmd58KMXZZZ2aT/gQx4a/mUk0tW0Bq6o4j 7HH2vvnfMNmja0s11tKqTrSFacm4ToLn+YMQBeQ4LvNQLS2Zuss6//vyCmt1nVZnFPJRGBrWiSlxI AXoMzyDg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kSHdA-0006sS-87; Tue, 13 Oct 2020 10:34:08 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id CE9D2300DB4; Tue, 13 Oct 2020 12:34:06 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BB6A82C1258F1; Tue, 13 Oct 2020 12:34:06 +0200 (CEST) Date: Tue, 13 Oct 2020 12:34:06 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: Boqun Feng , Qian Cai , Steven Rostedt , Ingo Molnar , x86 , linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org, Linux Next Mailing List , Stephen Rothwell Subject: Re: [tip: locking/core] lockdep: Fix lockdep recursion Message-ID: <20201013103406.GY2628@hirez.programming.kicks-ass.net> References: <160223032121.7002.1269740091547117869.tip-bot2@tip-bot2> <20201012031110.GA39540@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> <20201012212812.GH3249@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201012212812.GH3249@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-next@vger.kernel.org On Mon, Oct 12, 2020 at 02:28:12PM -0700, Paul E. McKenney wrote: > It is certainly an accident waiting to happen. Would something like > the following make sense? Sadly no. > ------------------------------------------------------------------------ > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index bfd38f2..52a63bc 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -4067,6 +4067,7 @@ void rcu_cpu_starting(unsigned int cpu) > > rnp = rdp->mynode; > mask = rdp->grpmask; > + lockdep_off(); > raw_spin_lock_irqsave_rcu_node(rnp, flags); > WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask); > newcpu = !(rnp->expmaskinitnext & mask); > @@ -4086,6 +4087,7 @@ void rcu_cpu_starting(unsigned int cpu) > } else { > raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > } > + lockdep_on(); > smp_mb(); /* Ensure RCU read-side usage follows above initialization. */ > } This will just shut it up, but will not fix the actual problem of that spin-lock ending up in trace_lock_acquire() which relies on RCU which isn't looking. What we need here is to supress tracing not lockdep. Let me consider.