From patchwork Fri Sep 13 16:35:07 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Dr. David Alan Gilbert" X-Patchwork-Id: 1162168 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 ozlabs.org (Postfix) with ESMTPS id 46VLqN4vSnz9sNF for ; Sat, 14 Sep 2019 02:36:00 +1000 (AEST) Received: from localhost ([::1]:46136 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8oYA-0002MC-HJ for incoming@patchwork.ozlabs.org; Fri, 13 Sep 2019 12:35:58 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35529) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8oXa-0002Jn-8L for qemu-devel@nongnu.org; Fri, 13 Sep 2019 12:35:23 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i8oXZ-0001pd-0k for qemu-devel@nongnu.org; Fri, 13 Sep 2019 12:35:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53226) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i8oXY-0001ox-Rm for qemu-devel@nongnu.org; Fri, 13 Sep 2019 12:35:20 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 26EFC81DE7 for ; Fri, 13 Sep 2019 16:35:20 +0000 (UTC) Received: from dgilbert-t580.localhost (unknown [10.36.118.12]) by smtp.corp.redhat.com (Postfix) with ESMTP id 48E5E60CC0; Fri, 13 Sep 2019 16:35:19 +0000 (UTC) From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, quintela@redhat.com, peterx@redhat.com Date: Fri, 13 Sep 2019 17:35:07 +0100 Message-Id: <20190913163507.1403-3-dgilbert@redhat.com> In-Reply-To: <20190913163507.1403-1-dgilbert@redhat.com> References: <20190913163507.1403-1-dgilbert@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Fri, 13 Sep 2019 16:35:20 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH 2/2] migration/rdma.c: Swap synchronize_rcu for call_rcu 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: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" From: "Dr. David Alan Gilbert" This fixes a deadlock that can occur on the migration source after a failed RDMA migration; as the source tries to cleanup it clears a pair of pointers and uses synchronize_rcu to wait; this is happening on the main thread. With the CPUs running a CPU thread can be an rcu reader and attempt to grab the main lock (kvm_handle_io->address_space_write->flatview_write->flatview_write_continue-> prepare_mmio_access->qemu_mutex_lock_iothread_impl) Replace the synchronize_rcu with a call_rcu to postpone the freeing. Fixes: 74637e6f08fceda98806 ("migration: implement bi-directional RDMA QIOChannel") ( https://bugzilla.redhat.com/show_bug.cgi?id=1746787 ) Signed-off-by: Dr. David Alan Gilbert --- migration/rdma.c | 39 +++++++++++++++++++++++++++------------ 1 file changed, 27 insertions(+), 12 deletions(-) diff --git a/migration/rdma.c b/migration/rdma.c index 0fcf02f48e..4c74e88a37 100644 --- a/migration/rdma.c +++ b/migration/rdma.c @@ -3017,11 +3017,35 @@ static void qio_channel_rdma_set_aio_fd_handler(QIOChannel *ioc, } } +struct rdma_close_rcu { + struct rcu_head rcu; + RDMAContext *rdmain; + RDMAContext *rdmaout; +}; + +/* callback from qio_channel_rdma_close via call_rcu */ +static void qio_channel_rdma_close_rcu(struct rdma_close_rcu *rcu) +{ + if (rcu->rdmain) { + qemu_rdma_cleanup(rcu->rdmain); + } + + if (rcu->rdmaout) { + qemu_rdma_cleanup(rcu->rdmaout); + } + + g_free(rcu->rdmain); + g_free(rcu->rdmaout); + g_free(rcu); +} + static int qio_channel_rdma_close(QIOChannel *ioc, Error **errp) { QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(ioc); RDMAContext *rdmain, *rdmaout; + struct rdma_close_rcu *rcu = g_new(struct rdma_close_rcu, 1); + trace_qemu_rdma_close(); rdmain = rioc->rdmain; @@ -3034,18 +3058,9 @@ static int qio_channel_rdma_close(QIOChannel *ioc, atomic_rcu_set(&rioc->rdmaout, NULL); } - synchronize_rcu(); - - if (rdmain) { - qemu_rdma_cleanup(rdmain); - } - - if (rdmaout) { - qemu_rdma_cleanup(rdmaout); - } - - g_free(rdmain); - g_free(rdmaout); + rcu->rdmain = rdmain; + rcu->rdmaout = rdmaout; + call_rcu(rcu, qio_channel_rdma_close_rcu, rcu); return 0; }