From patchwork Fri Oct 15 16:12:16 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kurz X-Patchwork-Id: 12562423 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 19097C433F5 for ; Fri, 15 Oct 2021 16:13:48 +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 C392A60551 for ; Fri, 15 Oct 2021 16:13:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org C392A60551 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kaod.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:40420 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mbPq6-00085B-Kh for qemu-devel@archiver.kernel.org; Fri, 15 Oct 2021 12:13:46 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:46844) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mbPor-0006Zo-Gq for qemu-devel@nongnu.org; Fri, 15 Oct 2021 12:12:29 -0400 Received: from us-smtp-delivery-44.mimecast.com ([205.139.111.44]:49936) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mbPop-000828-Kp for qemu-devel@nongnu.org; Fri, 15 Oct 2021 12:12:29 -0400 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-478-9D-Uf0B4PNSmKY3FHmXtSA-1; Fri, 15 Oct 2021 12:12:22 -0400 X-MC-Unique: 9D-Uf0B4PNSmKY3FHmXtSA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4AA1A362F9; Fri, 15 Oct 2021 16:12:21 +0000 (UTC) Received: from bahia.redhat.com (unknown [10.39.195.34]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9522D5F4E2; Fri, 15 Oct 2021 16:12:19 +0000 (UTC) From: Greg Kurz To: qemu-devel@nongnu.org Subject: [PATCH 0/2] accel/tcg: Fix monitor deadlock Date: Fri, 15 Oct 2021 18:12:16 +0200 Message-Id: <20211015161218.1231920-1-groug@kaod.org> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=groug@kaod.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kaod.org Received-SPF: softfail client-ip=205.139.111.44; envelope-from=groug@kaod.org; helo=us-smtp-delivery-44.mimecast.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_SOFTFAIL=0.665 autolearn=no 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: , Cc: Eduardo Habkost , Richard Henderson , Greg Kurz , qemu-stable@nongnu.org, Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Commit 7bed89958bfb ("device_core: use drain_call_rcu in in qmp_device_add") introduced a regression in QEMU 6.0 : passing device_add without argument hangs the monitor. This was reported against qemu-system-mips64 with TGC, but I could consistently reproduce it with other targets (x86 and ppc64). See https://gitlab.com/qemu-project/qemu/-/issues/650 for details. The problem is that an emulated busy-looping vCPU can stay forever in its RCU read-side critical section and prevent drain_call_rcu() to return. This series fixes the issue by letting RCU kick vCPUs out of the read-side critical section when drain_call_rcu() is in progress. This is achieved through notifiers, as suggested by Paolo Bonzini. Greg Kurz (2): rcu: Introduce force_rcu notifier accel/tcg: Register a force_rcu notifier accel/tcg/tcg-accel-ops-mttcg.c | 3 ++- accel/tcg/tcg-accel-ops-rr.c | 3 ++- accel/tcg/tcg-accel-ops.c | 11 +++++++++++ accel/tcg/tcg-accel-ops.h | 2 ++ include/hw/core/cpu.h | 2 ++ include/qemu/rcu.h | 21 ++++++++++++++++++++- util/rcu.c | 23 +++++++++++++++++++++-- 7 files changed, 60 insertions(+), 5 deletions(-)