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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 ECD92C49ED6 for ; Wed, 11 Sep 2019 18:50:38 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C10A22075C for ; Wed, 11 Sep 2019 18:50:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C10A22075C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:55554 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i87hN-000658-Q6 for qemu-devel@archiver.kernel.org; Wed, 11 Sep 2019 14:50:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:50558) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i87gj-0005Yf-G7 for qemu-devel@nongnu.org; Wed, 11 Sep 2019 14:49:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i87gg-0005Bb-Oo for qemu-devel@nongnu.org; Wed, 11 Sep 2019 14:49:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47652) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i87gg-0005BM-Im for qemu-devel@nongnu.org; Wed, 11 Sep 2019 14:49:54 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BF437307D945 for ; Wed, 11 Sep 2019 18:49:53 +0000 (UTC) Received: from work-vm (ovpn-117-243.ams2.redhat.com [10.36.117.243]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7CC235D9E2; Wed, 11 Sep 2019 18:49:52 +0000 (UTC) Date: Wed, 11 Sep 2019 19:49:50 +0100 From: "Dr. David Alan Gilbert" To: Eric Blake Message-ID: <20190911184950.GN2894@work-vm> References: <20190911164202.31136-1-dgilbert@redhat.com> <20190911164202.31136-2-dgilbert@redhat.com> <20190911165627.GG24295@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Wed, 11 Sep 2019 18:49:53 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: pbonzini@redhat.com, Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , qemu-devel@nongnu.org, quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Eric Blake (eblake@redhat.com) wrote: > On 9/11/19 11:56 AM, Daniel P. Berrang=E9 wrote: > > On Wed, Sep 11, 2019 at 05:42:00PM +0100, Dr. David Alan Gilbert (git= ) wrote: > >> From: "Dr. David Alan Gilbert" > >> > >> RCU_READ_LOCK_AUTO takes the rcu_read_lock and then uses glib's >=20 > spurious double space >=20 > >> g_auto infrastrcture (and thus whatever the compilers hooks are) to >=20 > infrastructure > compiler's Thanks. Dave > >> release it on all exits of the block. > >> > >> Note this macro has a variable declaration in, and hence is not in > >> a while loop. > >> >=20 > >> +#define RCU_READ_LOCK_AUTO g_auto(rcu_read_auto_t) \ > >> + _rcu_read_auto =3D 'x'; \ > >> + rcu_read_lock(); > >> + > >=20 > > Functionally this works, but my gut feeling would be to follow > > the design of GMutexLocker as-is: > >=20 > > https://developer.gnome.org/glib/stable/glib-Threads.html#g-mutex-l= ocker-new > >=20 > > so you get a use pattern of > >=20 > > g_autoptr(rcu_read_locker) locker =3D rcu_read_locker_new(); >=20 > Another pattern to consider: nbdkit uses: >=20 > #define ACQUIRE_LOCK_FOR_CURRENT_SCOPE(mutex) \ > CLEANUP_UNLOCK pthread_mutex_t *_lock =3D mutex; \ > do { \ > int _r =3D pthread_mutex_lock (_lock); \ > assert (!_r); \ > } while (0) >=20 > with later code calling: >=20 > ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&lock); >=20 > >=20 > > This makes it explicit that the code is creating a variable here, whi= ch > > in turns means it is clear to force unlock early with > >=20 > > g_clear_pointer(&locker, rcu_read_locker_free) >=20 > Yes, this aspect of glib is nicer than the corresponding nbdkit usage > pattern. >=20 > --=20 > Eric Blake, Principal Software Engineer > Red Hat, Inc. +1-919-301-3226 > Virtualization: qemu.org | libvirt.org >=20 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK