From nobody Sat Apr 12 11:17:24 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; 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 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1513697226610658.7884988204604; Tue, 19 Dec 2017 07:27:06 -0800 (PST) Received: from localhost ([::1]:49353 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eRJnH-0007fq-8q for importer@patchew.org; Tue, 19 Dec 2017 10:26:59 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58092) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eRJaD-0005EB-M0 for qemu-devel@nongnu.org; Tue, 19 Dec 2017 10:13:34 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eRJa7-0007NV-P2 for qemu-devel@nongnu.org; Tue, 19 Dec 2017 10:13:29 -0500 Received: from mx1.redhat.com ([209.132.183.28]:50754) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eRJa7-0007MZ-IK for qemu-devel@nongnu.org; Tue, 19 Dec 2017 10:13:23 -0500 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 C382E72D14; Tue, 19 Dec 2017 15:13:22 +0000 (UTC) Received: from localhost (ovpn-117-161.ams2.redhat.com [10.36.117.161]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0DEE26DA8B; Tue, 19 Dec 2017 15:13:17 +0000 (UTC) From: Stefan Hajnoczi To: Date: Tue, 19 Dec 2017 15:11:40 +0000 Message-Id: <20171219151144.11120-20-stefanha@redhat.com> In-Reply-To: <20171219151144.11120-1-stefanha@redhat.com> References: <20171219151144.11120-1-stefanha@redhat.com> 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 [10.5.110.27]); Tue, 19 Dec 2017 15:13:22 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PULL v2 19/23] docs: mark nested AioContext locking as a legacy API X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Stefan Hajnoczi Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" See the patch for why nested AioContext locking is no longer allowed. Signed-off-by: Stefan Hajnoczi Reviewed-by: Eric Blake Message-id: 20171207201320.19284-3-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi --- docs/devel/multiple-iothreads.txt | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/docs/devel/multiple-iothreads.txt b/docs/devel/multiple-iothre= ads.txt index e4d340bbb7..4f9012d154 100644 --- a/docs/devel/multiple-iothreads.txt +++ b/docs/devel/multiple-iothreads.txt @@ -1,4 +1,4 @@ -Copyright (c) 2014 Red Hat Inc. +Copyright (c) 2014-2017 Red Hat Inc. =20 This work is licensed under the terms of the GNU GPL, version 2 or later. = See the COPYING file in the top-level directory. @@ -92,8 +92,9 @@ aio_context_acquire()/aio_context_release() for mutual ex= clusion. Once the context is acquired no other thread can access it or run event loop iterat= ions in this AioContext. =20 -aio_context_acquire()/aio_context_release() calls may be nested. This -means you can call them if you're not sure whether #2 applies. +Legacy code sometimes nests aio_context_acquire()/aio_context_release() ca= lls. +Do not use nesting anymore, it is incompatible with the BDRV_POLL_WHILE() = macro +used in the block layer and can lead to hangs. =20 There is currently no lock ordering rule if a thread needs to acquire mult= iple AioContexts simultaneously. Therefore, it is only safe for code holding t= he --=20 2.14.3