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 A3D60C4332F for ; Thu, 9 Dec 2021 18:43:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229583AbhLISr2 (ORCPT ); Thu, 9 Dec 2021 13:47:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39896 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229487AbhLISrZ (ORCPT ); Thu, 9 Dec 2021 13:47:25 -0500 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9DB17C061746; Thu, 9 Dec 2021 10:43:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=4G3kmEjO1FSeu+BBXIYFvONCqu6PiAfYev3kCcCiBR4=; b=ySW6lxuhIFGTbZV5nCYgdOjV3s OgPi/kNLAx+BrGJ5PWvM4tiO6W6QiqRCVJsU9KxY1a+WKjwW1L2KpyQIJIlJ1gJtWXrXGaR+UO9Z3 I/2r7Tx0tFinNPDlGbAoWjns3+RIcYI7tzdssXBPIll8q/wAUzulCDLQQzkankYIq9tN3BHWXN7gl V16Yle3P9t5zrG+aOc7VYHzH6gqpMHOT4w1pRknCX1BXhpXsqKVGQeTr16zwllHyKpxBmg3hvHisv nF7rOd8ZApTug4+OJgKDyL1nmW+fBFGl4vl4jAN3q/vpSCh7/zwatNKofzdAvQoTdDiIK7PN6uhni rlX5FS5g==; Received: from 54-240-197-234.amazon.com ([54.240.197.234] helo=freeip.amazon.com) by bombadil.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mvOOE-00HGI5-UW; Thu, 09 Dec 2021 18:43:35 +0000 Message-ID: <3731b8da4dc46febc8adef331d6c97b21283428a.camel@infradead.org> Subject: Re: [PATCH 02/11] rcu: Kill rnp->ofl_seq and use only rcu_state.ofl_lock for exclusion From: David Woodhouse To: Neeraj Upadhyay , Thomas Gleixner Cc: Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Paolo Bonzini , "Paul E. McKenney" , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, rcu@vger.kernel.org, mimoja@mimoja.de, hewenliang4@huawei.com, hushiyuan@huawei.com, luolongjun@huawei.com, hejingxian@huawei.com Date: Thu, 09 Dec 2021 18:43:30 +0000 In-Reply-To: References: <20211209150938.3518-1-dwmw2@infradead.org> <20211209150938.3518-3-dwmw2@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-zjrVyy1PKK76w+1F/bJU" User-Agent: Evolution 3.36.5-0ubuntu1 MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-zjrVyy1PKK76w+1F/bJU Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2021-12-10 at 00:01 +0530, Neeraj Upadhyay wrote: > > @@ -4246,11 +4249,11 @@ void rcu_cpu_starting(unsigned int cpu) > > =20 > > rnp =3D rdp->mynode; > > mask =3D rdp->grpmask; > > - WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1); > > - WARN_ON_ONCE(!(rnp->ofl_seq & 0x1)); > > + local_irq_save(seq_flags); > > + arch_spin_lock(&rcu_state.ofl_lock); > > rcu_dynticks_eqs_online(); > > smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier(). >=20 > Can we drop this smp_mb(),as arch_spin_lock(&rcu_state.ofl_lock)=20 > provides the ordering now? Yes, thanks. > > - raw_spin_lock_irqsave_rcu_node(rnp, flags); > > + raw_spin_lock_rcu_node(rnp); > > WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask); > > newcpu =3D !(rnp->expmaskinitnext & mask); > > rnp->expmaskinitnext |=3D mask; > > @@ -4269,9 +4272,8 @@ void rcu_cpu_starting(unsigned int cpu) > > } else { > > raw_spin_unlock_irqrestore_rcu_node(rnp, flags); >=20 > 'flags' is uninitialized now? Ah yes, that suffered from the fact that saving the flags is pointless because we know we already disabled interrupts... but rcu_report_qs_rnp() *really* wants to be given some flags to restore. Will fix that too; thanks again. --=-zjrVyy1PKK76w+1F/bJU Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCECow ggUcMIIEBKADAgECAhEA4rtJSHkq7AnpxKUY8ZlYZjANBgkqhkiG9w0BAQsFADCBlzELMAkGA1UE BhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2FsZm9yZDEaMBgG A1UEChMRQ09NT0RPIENBIExpbWl0ZWQxPTA7BgNVBAMTNENPTU9ETyBSU0EgQ2xpZW50IEF1dGhl bnRpY2F0aW9uIGFuZCBTZWN1cmUgRW1haWwgQ0EwHhcNMTkwMTAyMDAwMDAwWhcNMjIwMTAxMjM1 OTU5WjAkMSIwIAYJKoZIhvcNAQkBFhNkd213MkBpbmZyYWRlYWQub3JnMIIBIjANBgkqhkiG9w0B AQEFAAOCAQ8AMIIBCgKCAQEAsv3wObLTCbUA7GJqKj9vHGf+Fa+tpkO+ZRVve9EpNsMsfXhvFpb8 RgL8vD+L133wK6csYoDU7zKiAo92FMUWaY1Hy6HqvVr9oevfTV3xhB5rQO1RHJoAfkvhy+wpjo7Q cXuzkOpibq2YurVStHAiGqAOMGMXhcVGqPuGhcVcVzVUjsvEzAV9Po9K2rpZ52FE4rDkpDK1pBK+ uOAyOkgIg/cD8Kugav5tyapydeWMZRJQH1vMQ6OVT24CyAn2yXm2NgTQMS1mpzStP2ioPtTnszIQ 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