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 67F28C3DA6E for ; Wed, 20 Dec 2023 16:34:05 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rFzVn-00055I-GB; Wed, 20 Dec 2023 11:33:36 -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 1rFzVi-00052H-7A for qemu-devel@nongnu.org; Wed, 20 Dec 2023 11:33:31 -0500 Received: from mgamail.intel.com ([192.198.163.11]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rFzVe-0006dr-7d for qemu-devel@nongnu.org; Wed, 20 Dec 2023 11:33:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1703090006; x=1734626006; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=sCKGWzuiKAuB607fgbj5++IPYoLBkWQCAgNuWkeqyd8=; b=B92FxQ0bmc8pmRyUUCe9MPuAJZpuXvxelwHAUFeG3H6ZQB7vHBMk3CfB tvLjBe7hvRgKhBh00E81+jOtKvdoLCphnRDVmcJeUUhF5Tdmu559MAJBR lJNLuWrYzkxjdrco3Wt7ofZzqem3Vx6CcUjnJDmMqczWvIcAR7OB1Vyfo DKxquZD+uZyBI1V2uAK62eFjKHj+Anqyr14oAfYxGu3PyMq7C5lAc0ZH9 eQJXvnstY8JJholKuo5Kbp0NjsZk0k/ZIDzM17S8scj1vOniRHTmCFzTh NlC/MJ91rOKeMANcQW3V5KVLr6DYQjMKXVAqyo0s4DN4r2a11HDMGKPgB g==; X-IronPort-AV: E=McAfee;i="6600,9927,10930"; a="2667185" X-IronPort-AV: E=Sophos;i="6.04,291,1695711600"; d="scan'208";a="2667185" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmvoesa105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Dec 2023 08:33:21 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10930"; a="726131820" X-IronPort-AV: E=Sophos;i="6.04,291,1695711600"; d="scan'208";a="726131820" Received: from liuzhao-optiplex-7080.sh.intel.com (HELO localhost) ([10.239.160.36]) by orsmga003.jf.intel.com with ESMTP; 20 Dec 2023 08:33:18 -0800 Date: Thu, 21 Dec 2023 00:46:03 +0800 From: Zhao Liu To: Markus Armbruster Cc: Akihiko Odaki , Paolo Bonzini , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Eduardo Habkost , qemu-devel@nongnu.org Subject: Re: [PATCH v2] qdev: Report an error for machine without HotplugHandler Message-ID: References: <20231210-bus-v2-1-34ebf5726fa0@daynix.com> <87h6kpgrl7.fsf@pond.sub.org> <8734vzsj6k.fsf@pond.sub.org> <87y1dpgvim.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87y1dpgvim.fsf@pond.sub.org> Received-SPF: pass client-ip=192.198.163.11; envelope-from=zhao1.liu@intel.com; helo=mgamail.intel.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, 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 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. > > 2. assert(dc->bus_type || !dc->hotpluggable) in a suitable spot. > > 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. > 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: static inline bool qdev_is_hotpluggable(DeviceState *dev) { /* * Many Machines don't implement qdev_hotplug_allowed(). * * TODO: Once all of them complete missing qdev_hotplug_allowed(), * use qdev_hotplug_allowed() here. */ bool hotpluggable = !!qdev_get_machine_hotplug_handler(dev); if (!hotpluggable && dev->parent_bus) { hotpluggable = qbus_is_hotpluggable(dev->parent_bus); } return hotpluggable; } Thanks, Zhao