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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 98912C433EF for ; Mon, 25 Oct 2021 14:18:40 +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 25DE260184 for ; Mon, 25 Oct 2021 14:18:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 25DE260184 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:51212 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mf0oA-0003vv-Rd for qemu-devel@archiver.kernel.org; Mon, 25 Oct 2021 10:18:38 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55514) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mf0lI-0001mB-Iu for qemu-devel@nongnu.org; Mon, 25 Oct 2021 10:15:41 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:24492) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mf0lE-0004Gv-5w for qemu-devel@nongnu.org; Mon, 25 Oct 2021 10:15:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1635171335; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=fjZLqrSmsERo2JEm8Ya/N0rqhRybtpyGBTRkFm9DbZY=; b=XhsqCB8JFymOZb5Ji5zUXZSEHEmk3Ou0O+x/ba9EHGSSYsE8PL8PAQ1XRY08D6F8r9Oqpn bcTQ8fla+5uBpRoBKGBaQsrQkL7CbhZYJk+9wSAJpcH7kn08mYpaYoApXNjWrCSEjwQLBm RrurDUZXGGPoTUVtvHugHV6cnPypT2U= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-165-kXcXTUCrOA63TeYrK2b1Fw-1; Mon, 25 Oct 2021 10:15:32 -0400 X-MC-Unique: kXcXTUCrOA63TeYrK2b1Fw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 957EB101F01F; Mon, 25 Oct 2021 14:15:31 +0000 (UTC) Received: from redhat.com (unknown [10.39.195.59]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4A2C179451; Mon, 25 Oct 2021 14:14:38 +0000 (UTC) Date: Mon, 25 Oct 2021 15:14:36 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Stefan Hajnoczi Subject: Re: [RFC 1/2] tls: add macros for coroutine-safe TLS variables Message-ID: References: <20211025140716.166971-1-stefanha@redhat.com> <20211025140716.166971-2-stefanha@redhat.com> MIME-Version: 1.0 In-Reply-To: <20211025140716.166971-2-stefanha@redhat.com> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: fweimer@redhat.com, Kevin Wolf , thuth@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, Fam Zheng , sguelton@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Oct 25, 2021 at 03:07:15PM +0100, Stefan Hajnoczi wrote: > Compiler optimizations can cache TLS values across coroutine yield > points, resulting in stale values from the previous thread when a > coroutine is re-entered by a new thread. > > Serge Guelton developed an __attribute__((noinline)) wrapper and tested > it with clang and gcc. I formatted his idea according to QEMU's coding > style and wrote documentation. > > These macros must be used instead of __thread from now on to prevent > coroutine TLS bugs. Does this apply to all __thread usage in the QEMU process that can be used from coroutine context, or just certain __thread usage ? Mostly I'm wondering if this is going to have implications on external libraries we use. eg if block layer is using librbd.so APIs, is librbd.sp safe to use __thread directly in any way it desires ? Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|