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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id B6460C35274 for ; Thu, 21 Dec 2023 08:50:18 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rGEk9-0007wv-Pi; Thu, 21 Dec 2023 03:49:25 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rGEk8-0007vD-UJ for qemu-devel@nongnu.org; Thu, 21 Dec 2023 03:49:24 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rGEk6-00030Z-Uz for qemu-devel@nongnu.org; Thu, 21 Dec 2023 03:49:24 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1703148561; 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: in-reply-to:in-reply-to:references:references; bh=D1MZ7n+0ATSpNn9T1QWfP3GWKRPCY+A7Fw432VQncHI=; b=PmBE5KVGPZWl2jTPYhspXo13ge9RJ9/VtOM/lw5zABHc6ESY6aG/vJUjfk8R74/aJNhnai daXMO94b1a914HtUS95ikQNq85uvRmf1Tf77U/vKD/Ik2owyr8frB7O4MBH2oo8H6gWRO1 +jRaoPIzYBWc6RAgmeCOor35dWQizPk= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-378-_PoA2BjDPlm6-vUnO7wRQQ-1; Thu, 21 Dec 2023 03:49:17 -0500 X-MC-Unique: _PoA2BjDPlm6-vUnO7wRQQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3133585A58B; Thu, 21 Dec 2023 08:49:17 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.129]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E77CD51D5; Thu, 21 Dec 2023 08:49:16 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id AEFAF21E6920; Thu, 21 Dec 2023 09:49:15 +0100 (CET) From: Markus Armbruster To: Akihiko Odaki Cc: Zhao Liu , Paolo Bonzini , Daniel P. =?utf-8?Q?Berrang=C3=A9?= , Eduardo Habkost , qemu-devel@nongnu.org Subject: Re: [PATCH v2] qdev: Report an error for machine without HotplugHandler In-Reply-To: <68c2e155-0dc1-4566-853a-059e351e9649@daynix.com> (Akihiko Odaki's message of "Thu, 21 Dec 2023 15:36:32 +0900") References: <20231210-bus-v2-1-34ebf5726fa0@daynix.com> <87h6kpgrl7.fsf@pond.sub.org> <8734vzsj6k.fsf@pond.sub.org> <87y1dpgvim.fsf@pond.sub.org> <68c2e155-0dc1-4566-853a-059e351e9649@daynix.com> Date: Thu, 21 Dec 2023 09:49:15 +0100 Message-ID: <87ttoc6ius.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@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=-0.063, 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_H3=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=ham 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Akihiko Odaki writes: > On 2023/12/21 1:46, Zhao Liu wrote: >> Hi Markus, >> On Wed, Dec 20, 2023 at 08:53:21AM +0100, Markus Armbruster wrote: >>> Date: Wed, 20 Dec 2023 08:53:21 +0100 >>> From: Markus Armbruster >>> Subject: Re: [PATCH v2] qdev: Report an error for machine without >>> HotplugHandler >>> >>> Akihiko Odaki writes: >>> >>>> On 2023/12/18 23:02, Markus Armbruster wrote: >>>>> Akihiko Odaki writes: >>>>> >>>>>> On 2023/12/11 15:51, Markus Armbruster wrote: >>>>>>> Akihiko Odaki writes: >>>>>>> >>>>>>>> The HotplugHandler of the machine will be used when the parent bus does >>>>>>>> not exist, but the machine may not have one. Report an error in such a >>>>>>>> case instead of aborting. >>>>>>>> >>>>>>>> Fixes: 7716b8ca74 ("qdev: HotplugHandler: Add support for unplugging BUS-less devices") >>>>>>>> Signed-off-by: Akihiko Odaki >>>>>>> >>>>>>> Do you have a reproducer for the crash? >>>>>>> >>>>>>>> --- >>>>>>>> Changes in v2: >>>>>>>> - Fixed indention. >>>>>>>> - Link to v1: https://lore.kernel.org/r/20231202-bus-v1-1-f7540e3a8d62@daynix.com >>>>>>>> --- >>>>>>>> system/qdev-monitor.c | 13 ++++++++++--- >>>>>>>> 1 file changed, 10 insertions(+), 3 deletions(-) >>>>>>>> >>>>>>>> diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c >>>>>>>> index a13db763e5..5fe5d49c20 100644 >>>>>>>> --- a/system/qdev-monitor.c >>>>>>>> +++ b/system/qdev-monitor.c >>>>>>>> @@ -927,9 +927,16 @@ void qdev_unplug(DeviceState *dev, Error **errp) >>>>>>> void qdev_unplug(DeviceState *dev, Error **errp) >>>>>>> { >>>>>>> DeviceClass *dc = DEVICE_GET_CLASS(dev); >>>>>>> HotplugHandler *hotplug_ctrl; >>>>>>> HotplugHandlerClass *hdc; >>>>>>> Error *local_err = NULL; >>>>>>> if (qdev_unplug_blocked(dev, errp)) { >>>>>>> return; >>>>>>> } >>>>>>> if (dev->parent_bus && !qbus_is_hotpluggable(dev->parent_bus)) { >>>>>>> error_setg(errp, QERR_BUS_NO_HOTPLUG, dev->parent_bus->name); >>>>>>> return; >>>>>>> } >>>>>>> if (!dc->hotpluggable) { >>>>>>> error_setg(errp, QERR_DEVICE_NO_HOTPLUG, >>>>>>> object_get_typename(OBJECT(dev))); >>>>>>> return; >>>>>>> } >>>>>>> if (!migration_is_idle() && !dev->allow_unplug_during_migration) { >>>>>>> error_setg(errp, "device_del not allowed while migrating"); >>>>>>> return; >>>>>>> } >>>>>>> >>>>>>>> qdev_hot_removed = true; >>>>>>>> hotplug_ctrl = qdev_get_hotplug_handler(dev); >>>>>>>> - /* hotpluggable device MUST have HotplugHandler, if it doesn't >>>>>>>> - * then something is very wrong with it */ >>>>>>>> - g_assert(hotplug_ctrl); >>>>>>>> + if (!hotplug_ctrl) { >>>>>>>> + /* >>>>>>>> + * hotpluggable bus MUST have HotplugHandler, if it doesn't >>>>>>>> + * then something is very wrong with it >>>>>>>> + */ >>>>>>>> + assert(!dev->parent_bus); >>>>>>>> + >>>>>>>> + error_setg(errp, "The machine does not support hotplugging for a device without parent bus"); >>>>>>>> + return; >>>>>>>> + } >>>>>>> >>>>>>> Extended version of my question above: what are the devices where >>>>>>> qdev_get_hotplug_handler(dev) returns null here? >>>>>> >>>>>> Start a VM: qemu-system-aarch64 -M virt -nographic >>>>>> Run the following on its HMP: device_del /machine/unattached/device[0] >>>>>> >>>>>> It tries to unplug cortex-a15-arm-cpu and crashes. >>>>> >>>>> This device has no parent bus (dev->parent_bus is null), but is marked >>>>> hot-pluggable (dc->hotpluggable is true). Question for somebody >>>>> familiar with the hot-plug machinery: is this sane? >>>> >>>> Setting hotpluggable false for each device without bus_type gives the same effect, but is error-prone. >>> >>> Having hotpluggable = true when the device cannot be hot-plugged is >>> *wrong*. You might be able to paper over the wrongness so the code >>> works anyway, but nothing good can come out of lying to developers >>> trying to understand how the code works. >>> >>> Three ideas to avoid the lying: >>> >>> 1. default hotpluggable to bus_type != NULL. > > I don't have an idea to achieve that. Currently bus_type is set after hotpluggable. > >>> >>> 2. assert(dc->bus_type || !dc->hotpluggable) in a suitable spot. > > It results in abortion and doesn't improve the situation. Oh, it does! The abort leads us to all the places where we currently lie (by having dc->hotpluggable = true when it isn't), so we can fix them. >>> 3. Change the meaning of hotpluggable, and rename it to reflect its new >>> meaning. Requires a careful reading of its uses. I wouldn't go there. > > I don't have an idea for such a naming. > > So I'm stuck with the current proposal. It suppresses abortion at least. Any alternative idea is welcome. > >>> >> What about 4 (or maybe 3.1) - droping this hotpluggable flag and just use a >> helper (like qbus) to check if device is hotpluggable? >> This removes the confusion of that flag and also reduces the number of >> configuration items for DeviceState that require developer attention. >> A simple helper is as follows: > > Some devices simply doesn't support hotplugging even if the bus supports. virtio-gpu-pci doesn't support hotplugging because the display infrastructure cannot handle hotplugging, for example. > > Regards, > Akihiko Odaki