From nobody Sun Feb 8 03:57:54 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1570459142; cv=none; d=zoho.com; s=zohoarc; b=oCZTpftQekX1xy8Kd97adErsGU467hI+zwnCL8A68KDsa1ZYw+tXOk8ShGPvSYu7947APJPHBCEJ+1WgBU/RUsiMjvlXKD6/Yv07ow8T6dX46X86eI5dzbBp0npPjBNZn1AcPgHDc4D67iCGSgxu9u7ptCJ1zk6s4ulDRlSqB8Q= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; s=zohoarc; t=1570459142; h=Content-Type:Content-Transfer-Encoding:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:To:ARC-Authentication-Results; bh=BeL+kT/cShNB5IWwrn1P26Q5rVZI4WKKIj9+t/10bS8=; b=itrU8Z4nVbrZ/FfyO590RvAl22wckURGG1ejy2FLvHWQ4YoW/uB4zm5lFsCOhUn+QqjDoF5ZIC4wyM2y2+CrEam3Sj+yBWzpOEG7uQtiooUb7ICq3X6VbnM/Ul6KCxnL85HmsI7ZCQiBywLklPe9FiSuoPQAy6cdAS/raydLrak= ARC-Authentication-Results: i=1; mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1570459142060383.66618231234213; Mon, 7 Oct 2019 07:39:02 -0700 (PDT) Received: from localhost ([::1]:45580 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iHUA8-0005zl-HO for importer@patchew.org; Mon, 07 Oct 2019 10:39:00 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41210) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iHU81-0003yI-BH for qemu-devel@nongnu.org; Mon, 07 Oct 2019 10:36:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iHU7z-0005QW-Rh for qemu-devel@nongnu.org; Mon, 07 Oct 2019 10:36:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37828) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iHU7z-0005Q7-JM for qemu-devel@nongnu.org; Mon, 07 Oct 2019 10:36:47 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C2FDC308FBAC for ; Mon, 7 Oct 2019 14:36:46 +0000 (UTC) Received: from dgilbert-t580.localhost (ovpn-117-145.ams2.redhat.com [10.36.117.145]) by smtp.corp.redhat.com (Postfix) with ESMTP id E916360C05; Mon, 7 Oct 2019 14:36:45 +0000 (UTC) From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, pbonzini@redhat.com, berrange@redhat.com Subject: [PATCH v4 1/5] rcu: Add automatically released rcu_read_lock variants Date: Mon, 7 Oct 2019 15:36:37 +0100 Message-Id: <20191007143642.301445-2-dgilbert@redhat.com> In-Reply-To: <20191007143642.301445-1-dgilbert@redhat.com> References: <20191007143642.301445-1-dgilbert@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Mon, 07 Oct 2019 14:36:46 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 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: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Type: text/plain; charset="utf-8" From: "Dr. David Alan Gilbert" RCU_READ_LOCK_GUARD() takes the rcu_read_lock and then uses glib's g_auto infrastructure (and thus whatever the compiler's hooks are) to release it on all exits of the block. WITH_RCU_READ_LOCK_GUARD() is similar but is used as a wrapper for the lock, i.e.: WITH_RCU_READ_LOCK_GUARD() { stuff under lock } Note the 'unused' attribute is needed to work around clang bug: https://bugs.llvm.org/show_bug.cgi?id=3D43482 Signed-off-by: Dr. David Alan Gilbert Acked-by: Paolo Bonzini Reviewed-by: Daniel P. Berrang=C3=A9 --- docs/devel/rcu.txt | 16 ++++++++++++++++ include/qemu/rcu.h | 25 +++++++++++++++++++++++++ 2 files changed, 41 insertions(+) diff --git a/docs/devel/rcu.txt b/docs/devel/rcu.txt index c84e7f42b2..d83fed2f79 100644 --- a/docs/devel/rcu.txt +++ b/docs/devel/rcu.txt @@ -187,6 +187,22 @@ The following APIs must be used before RCU is used in = a thread: Note that these APIs are relatively heavyweight, and should _not_ be nested. =20 +Convenience macros +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +Two macros are provided that automatically release the read lock at the +end of the scope. + + RCU_READ_LOCK_GUARD() + + Takes the lock and will release it at the end of the block it's + used in. + + WITH_RCU_READ_LOCK_GUARD() { code } + + Is used at the head of a block to protect the code within the blo= ck. + +Note that 'goto'ing out of the guarded block will also drop the lock. =20 DIFFERENCES WITH LINUX =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h index 22876d1428..9c82683e37 100644 --- a/include/qemu/rcu.h +++ b/include/qemu/rcu.h @@ -154,6 +154,31 @@ extern void call_rcu1(struct rcu_head *head, RCUCBFunc= *func); }), \ (RCUCBFunc *)g_free); =20 +typedef void RCUReadAuto; +static inline RCUReadAuto *rcu_read_auto_lock(void) +{ + rcu_read_lock(); + /* Anything non-NULL causes the cleanup function to be called */ + return (void *)(uintptr_t)0x1; +} + +static inline void rcu_read_auto_unlock(RCUReadAuto *r) +{ + rcu_read_unlock(); +} + +G_DEFINE_AUTOPTR_CLEANUP_FUNC(RCUReadAuto, rcu_read_auto_unlock) + +#define WITH_RCU_READ_LOCK_GUARD() \ + WITH_RCU_READ_LOCK_GUARD_(_rcu_read_auto##__COUNTER__) + +#define WITH_RCU_READ_LOCK_GUARD_(var) \ + for (g_autoptr(RCUReadAuto) var =3D rcu_read_auto_lock(); \ + (var); rcu_read_auto_unlock(var), (var) =3D NULL) + +#define RCU_READ_LOCK_GUARD() \ + g_autoptr(RCUReadAuto) _rcu_read_auto __attribute__((unused)) =3D rcu_= read_auto_lock() + #ifdef __cplusplus } #endif --=20 2.23.0