From patchwork Tue Nov 9 18:35:21 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kurz X-Patchwork-Id: 12610999 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 0D001C433EF for ; Tue, 9 Nov 2021 18:36:54 +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 AA3E561179 for ; Tue, 9 Nov 2021 18:36:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org AA3E561179 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]:39716 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mkVzI-00053O-Ou for qemu-devel@archiver.kernel.org; Tue, 09 Nov 2021 13:36:52 -0500 Received: from eggs.gnu.org ([209.51.188.92]:55920) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mkVy1-0003LJ-Be for qemu-devel@nongnu.org; Tue, 09 Nov 2021 13:35:33 -0500 Received: from us-smtp-delivery-44.mimecast.com ([207.211.30.44]:37623) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mkVxz-0001LY-P0 for qemu-devel@nongnu.org; Tue, 09 Nov 2021 13:35:33 -0500 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-335-_UlVLABiMkyklqaybUMyFQ-1; Tue, 09 Nov 2021 13:35:28 -0500 X-MC-Unique: _UlVLABiMkyklqaybUMyFQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E6A2E87D541; Tue, 9 Nov 2021 18:35:26 +0000 (UTC) Received: from bahia.redhat.com (unknown [10.39.194.211]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7502D60936; Tue, 9 Nov 2021 18:35:24 +0000 (UTC) From: Greg Kurz To: qemu-devel@nongnu.org Subject: [PATCH v4 0/2] accel/tcg: Fix monitor deadlock Date: Tue, 9 Nov 2021 19:35:21 +0100 Message-Id: <20211109183523.47726-1-groug@kaod.org> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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=207.211.30.44; 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: 2.1.29 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 vCPU threads out of the read-side critical section when drain_call_rcu() is in progress. This is achieved through notifiers, as suggested by Paolo Bonzini. I've pushed this series to: https://gitlab.com/gkurz/qemu/-/commits/fix-drain-call-rcu v4: - use rr_kick_next_cpu() instead of async_run_on_cpu(first_cpu) v3: - new separate implementations of force RCU notifiers for MTTCG and RR v2: - moved notifier list to RCU reader data - separate API for notifier registration - CPUState passed as an opaque pointer Greg Kurz (2): rcu: Introduce force_rcu notifier accel/tcg: Register a force_rcu notifier accel/tcg/tcg-accel-ops-mttcg.c | 26 ++++++++++++++++++++++++++ accel/tcg/tcg-accel-ops-rr.c | 10 ++++++++++ include/qemu/rcu.h | 15 +++++++++++++++ util/rcu.c | 19 +++++++++++++++++++ 4 files changed, 70 insertions(+)