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 8BC83C433EF for ; Mon, 13 Dec 2021 08:18:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232808AbhLMISi (ORCPT ); Mon, 13 Dec 2021 03:18:38 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36136 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229483AbhLMISh (ORCPT ); Mon, 13 Dec 2021 03:18:37 -0500 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 61FE7C06173F; Mon, 13 Dec 2021 00:18:37 -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=U8pkhJ5nScbcgED8kG12igkAidYQl/E5bMAgaJ/P6t8=; b=eBzMn0IdWjCFiV8wxk3d3U96CP tVGp6WxrGCga1X3+AXRlAc0VguWblOHpZhFC4hccKcS3fJy1yAPsHu0oZd/mngWpqNdBzdpmaM24+ P46Adw8YSY76jqogIIGiXb8A2F/2Z/l36fGUAUHIO6FOJQX9Liq/IEfAav6XO0oGohsu3FZASwCWY AYHlKNxKyJMLRA6fXbCv3f+pl76zb4n8Ck2SOLXXgMoHbtv6FFJPNBy4cDoqgAmq+INMpwmsRI8Do XbwlG/TKhj6WF7C4XVZzwDVuQQUgYUcs+1yL8pmBqAT6eYLCPdKW3RGwgansx+D32SzHMYhX4muwQ ZZ7l3lnQ==; Received: from [2001:8b0:10b:1::3ae] (helo=u3832b3a9db3152.ant.amazon.com) by bombadil.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mwgXH-008GxQ-Tu; Mon, 13 Dec 2021 08:18:16 +0000 Message-ID: <6c184b9ffc5c641736d53bb7598f814d6b4c3fe0.camel@infradead.org> Subject: Re: [EXTERNAL] [PATCH v2] rcu/nocb: Handle concurrent nocb kthreads creation From: David Woodhouse To: Neeraj Upadhyay , paulmck@kernel.org, frederic@kernel.org, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, joel@joelfernandes.org Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, urezki@gmail.com, boqun.feng@gmail.com Date: Mon, 13 Dec 2021 08:18:11 +0000 In-Reply-To: <20211211170139.27711-1-quic_neeraju@quicinc.com> References: <20211211170139.27711-1-quic_neeraju@quicinc.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-WcodL/RAUfxnppsGSZ6R" 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 --=-WcodL/RAUfxnppsGSZ6R Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sat, 2021-12-11 at 22:31 +0530, Neeraj Upadhyay wrote: > When multiple CPUs in the same nocb gp/cb group concurrently > come online, they might try to concurrently create the same > rcuog kthread. Fix this by using nocb gp CPU's spawn mutex to > provide mutual exclusion for the rcuog kthread creation code. >=20 > Signed-off-by: Neeraj Upadhyay > --- > Change in v2: > Fix missing mutex_unlock in nocb gp kthread creation err path. I think this ends up being not strictly necessary in the short term too because we aren't currently planning to run rcutree_prepare_cpu() concurrently anyway. But harmless and worth fixing in the longer term. Although, if I've already added a mutex for adding the boost thread, could we manage to use the *same* mutex instead of adding another one? Acked-by: David Woodhouse + mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); > return; > + } > WRITE_ONCE(rdp_gp->nocb_gp_kthread, t); > } > + mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); >=20 > /* Spawn the kthread for this CPU. */ Some whitespace damage there. --=-WcodL/RAUfxnppsGSZ6R 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 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