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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 E0BCFC2BB85 for ; Thu, 16 Apr 2020 08:29:48 +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 AB3EA2076A for ; Thu, 16 Apr 2020 08:29:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="NhQuuMO7" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB3EA2076A 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]:59304 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jOzu7-0000TK-Nr for qemu-devel@archiver.kernel.org; Thu, 16 Apr 2020 04:29:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45544) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jOztT-00083q-4x for qemu-devel@nongnu.org; Thu, 16 Apr 2020 04:29:08 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jOztR-0005wq-ON for qemu-devel@nongnu.org; Thu, 16 Apr 2020 04:29:06 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:60685 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jOztR-0005vd-Ja for qemu-devel@nongnu.org; Thu, 16 Apr 2020 04:29:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587025744; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=RxdmOOlDmbharo4ox9UEiQ+zPxmF8XXugYEGG9AFjxk=; b=NhQuuMO7y9AnRWEzIEyWV87nYBVEDVwk6rxBhupbAA8728YeZ3OlI+tl0ZOX0/pJsHEEqt CFiL4HPSX9bnTwUfIXO7PxsWkJUxrEF3qUwrhM5RMw2pD+OprHntDjf55HQlTU6ePKX0VV oF1Y6uZ2Y6DoO2TTBkcgKlYpGhL2W5k= 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-188-0xcXpKZ6MEWIzfbABrifMQ-1; Thu, 16 Apr 2020 04:29:00 -0400 X-MC-Unique: 0xcXpKZ6MEWIzfbABrifMQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8AC2F19251A0; Thu, 16 Apr 2020 08:28:59 +0000 (UTC) Received: from linux.fritz.box (ovpn-113-109.ams2.redhat.com [10.36.113.109]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3E7767E7C0; Thu, 16 Apr 2020 08:28:50 +0000 (UTC) Date: Thu, 16 Apr 2020 10:28:49 +0200 From: Kevin Wolf To: Stefan Reiter Subject: Re: qemu_coroutine_yield switches thread? Message-ID: <20200416082849.GA6014@linux.fritz.box> References: <5dde1955-49db-2626-1fa5-332e4d7a0928@proxmox.com> MIME-Version: 1.0 In-Reply-To: <5dde1955-49db-2626-1fa5-332e4d7a0928@proxmox.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 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: vsementsov@virtuozzo.com, slp@redhat.com, "qemu-devel@nongnu.org" , mreitz@redhat.com, stefanha@redhat.com, jsnow@redhat.com, dietmar@proxmox.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 16.04.2020 um 10:06 hat Stefan Reiter geschrieben: > Hi list, >=20 > quick question: Can a resume from a qemu_coroutine_yield happen in a > different thread? >=20 > Well, it can, since I'm seeing it happen, but is that okay or a bug? Yes, it can happen. At least for devices like IDE where a request is started during a vmexit (MMIO or I/O port write), the coroutine will usually begin its life in the vcpu thread and then move to the main loop thread. This is not a problem because the vcpu thread holds the BQL while running the request coroutine. > I.e. in a backup-job the following can sporadically trip: >=20 > unsigned long tid =3D pthread_self(); > qemu_get_current_aio_context(); // returns main context > qemu_coroutine_yield(); > qemu_get_current_aio_context(); // still returns main context, but: > assert(tid =3D=3D pthread_self()); // this fails >=20 > It seems to be called from a vCPU thread when it happens. VM uses no > iothreads. This must be a guest request that was intercepted by the backup job. I think it wouldn't happen for the background copy, these requests already start in the main loop. Kevin