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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 33B2CC3A5A6 for ; Thu, 19 Sep 2019 11:55:35 +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 08AB421924 for ; Thu, 19 Sep 2019 11:55:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 08AB421924 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; 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Thu, 19 Sep 2019 11:38:12 +0000 (UTC) Received: from localhost.localdomain (unknown [10.36.116.255]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7B87B5D9E5; Thu, 19 Sep 2019 11:38:02 +0000 (UTC) Date: Thu, 19 Sep 2019 13:38:01 +0200 From: Kevin Wolf To: Sergio Lopez Message-ID: <20190919113801.GD10163@localhost.localdomain> References: <20190916112411.21636-1-slp@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190916112411.21636-1-slp@redhat.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.68]); Thu, 19 Sep 2019 11:38:12 +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: Re: [Qemu-devel] [PATCH v3] virtio-blk: schedule virtio_notify_config to run on main context 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: mreitz@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org, mst@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 16.09.2019 um 13:24 hat Sergio Lopez geschrieben: > virtio_notify_config() needs to acquire the global mutex, which isn't > allowed from an iothread, and may lead to a deadlock like this: > > - main thead > * Has acquired: qemu_global_mutex. > * Is trying the acquire: iothread AioContext lock via > AIO_WAIT_WHILE (after aio_poll). > > - iothread > * Has acquired: AioContext lock. > * Is trying to acquire: qemu_global_mutex (via > virtio_notify_config->prepare_mmio_access). > > If virtio_blk_resize() is called from an iothread, schedule > virtio_notify_config() to be run in the main context BH. > > Signed-off-by: Sergio Lopez > --- > Changelog > > v3: > - Unconditionally schedule the work to be done in the main context BH > (thanks John Snow and Kevin Wolf). > > v2: > - Use aio_bh_schedule_oneshot instead of scheduling a coroutine > (thanks Kevin Wolf). > - Switch from RFC to v2 patch. > --- > hw/block/virtio-blk.c | 17 ++++++++++++++++- > 1 file changed, 16 insertions(+), 1 deletion(-) > > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c > index 18851601cb..0163285f6f 100644 > --- a/hw/block/virtio-blk.c > +++ b/hw/block/virtio-blk.c > @@ -16,6 +16,7 @@ > #include "qemu/iov.h" > #include "qemu/module.h" > #include "qemu/error-report.h" > +#include "qemu/main-loop.h" > #include "trace.h" > #include "hw/block/block.h" > #include "hw/qdev-properties.h" > @@ -1086,11 +1087,25 @@ static int virtio_blk_load_device(VirtIODevice *vdev, QEMUFile *f, > return 0; > } > > +static void virtio_resize_cb(void *opaque) > +{ > + VirtIODevice *vdev = opaque; > + > + assert(qemu_get_current_aio_context() == qemu_get_aio_context()); > + virtio_notify_config(vdev); > +} > + > static void virtio_blk_resize(void *opaque) > { > VirtIODevice *vdev = VIRTIO_DEVICE(opaque); > > - virtio_notify_config(vdev); > + /* > + * virtio_notify_config() needs to acquire the global mutex, > + * so it can't be called from an iothread. Instead, schedule > + * it to be run in the main context BH. > + */ > + aio_bh_schedule_oneshot(qemu_get_aio_context(), > + virtio_resize_cb, vdev); This fits on a single line. With this fixed: Reviewed-by: Kevin Wolf