From nobody Mon Sep 22 23:40:27 2025 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.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 Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1647264191578205.94665790020974; Mon, 14 Mar 2022 06:23:11 -0700 (PDT) Received: from localhost ([::1]:36284 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nTkfG-0004ZU-D2 for importer@patchew.org; Mon, 14 Mar 2022 09:23:10 -0400 Received: from eggs.gnu.org ([209.51.188.92]:38134) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nTkbU-0001N4-Ud for qemu-devel@nongnu.org; Mon, 14 Mar 2022 09:19:17 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:28563) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nTkbR-0006ab-Vc for qemu-devel@nongnu.org; Mon, 14 Mar 2022 09:19:15 -0400 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-628-IILUMor1P1qvW0I67Zj9FA-1; Mon, 14 Mar 2022 09:19:07 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E351E3802AC2; Mon, 14 Mar 2022 13:19:06 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id A13141686D; Mon, 14 Mar 2022 13:19:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647263953; 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=Kjw9Nxjqxr/9vvEq1d2PrrSV5wW1BVe9jUPxonmNzko=; b=Uvv2vOixCXl57UIhd35iFHThk+UVJN9AjpfWKzGV84eZe9Aw0SkF2NLVO4uRhxv4USnFo0 90NZvUcYmwOtWrZosskQPV2K3+IJ88Ef7ClNjipRKdbjRpuyf6p9OjzMDvyDBodvw9xYJY 60bIitGR2zLKOu2ME7vkQlYVGJ9h9MM= X-MC-Unique: IILUMor1P1qvW0I67Zj9FA-1 From: Emanuele Giuseppe Esposito To: qemu-block@nongnu.org Subject: [PATCH v2 09/10] child_job_drained_poll: override polling condition only when in home thread Date: Mon, 14 Mar 2022 09:18:53 -0400 Message-Id: <20220314131854.2202651-10-eesposit@redhat.com> In-Reply-To: <20220314131854.2202651-1-eesposit@redhat.com> References: <20220314131854.2202651-1-eesposit@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eesposit@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.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; Received-SPF: pass client-ip=170.10.133.124; envelope-from=eesposit@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Fam Zheng , Vladimir Sementsov-Ogievskiy , Emanuele Giuseppe Esposito , qemu-devel@nongnu.org, Hanna Reitz , Stefan Hajnoczi , Paolo Bonzini , John Snow Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) X-ZM-MESSAGEID: 1647264194713100005 Content-Type: text/plain; charset="utf-8" drv->drained_poll() is only implemented in mirror, and allows it to drain from within the coroutine. The mirror implementation uses in_drain flag to recognize when it is draining from coroutine, and consequently avoid deadlocking (wait the poll condition in child_job_drained_poll to wait for itself). The problem is that this flag is dangerous, because it breaks bdrv_drained_begin() invariants: once drained_begin ends, all jobs, in_flight requests, and anything running in the iothread are blocked. This can be broken in such way: iothread(mirror): s->in_drain =3D true; // mirror.c:1112 main loop: bdrv_drained_begin(mirror_bs); /* * drained_begin wait for bdrv_drain_poll_top_level() condition, * that translates in child_job_drained_poll() for jobs, but * mirror implements drv->drained_poll() so it returns * !!in_flight_requests, which his 0 (assertion in mirror.c:1105). */ main loop: thinks iothread is stopped and is modifying the graph... iothread(mirror): *continues*, as nothing is stopping it iothread(mirror): bdrv_drained_begin(bs); /* draining reads the graph while it is modified!! */ main loop: done modifying the graph... In order to fix this, we can simply allow drv->drained_poll() to be called only by the iothread, and not the main loop. We distinguish it by using in_aio_context_home_thread(), that returns false if @ctx is not the same as the thread that runs it. Co-Developed-by: Paolo Bonzini Signed-off-by: Emanuele Giuseppe Esposito --- blockjob.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/blockjob.c b/blockjob.c index 4868453d74..14a919b3cc 100644 --- a/blockjob.c +++ b/blockjob.c @@ -110,7 +110,9 @@ static bool child_job_drained_poll(BdrvChild *c) BlockJob *bjob =3D c->opaque; Job *job =3D &bjob->job; const BlockJobDriver *drv =3D block_job_driver(bjob); + AioContext *ctx; =20 + ctx =3D job->aio_context; /* An inactive or completed job doesn't have any pending requests. Jobs * with !job->busy are either already paused or have a pause point aft= er * being reentered, so no job driver code will run before they pause. = */ @@ -118,9 +120,14 @@ static bool child_job_drained_poll(BdrvChild *c) return false; } =20 - /* Otherwise, assume that it isn't fully stopped yet, but allow the jo= b to - * override this assumption. */ - if (drv->drained_poll) { + /* + * Otherwise, assume that it isn't fully stopped yet, but allow the jo= b to + * override this assumption, if the drain is being performed in the + * iothread. We need to check that the caller is the home thread becau= se + * it could otherwise lead the main loop to exit polling while the job + * has not paused yet. + */ + if (in_aio_context_home_thread(ctx) && drv->drained_poll) { return drv->drained_poll(bjob); } else { return true; --=20 2.31.1