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Mon, 12 Oct 2020 20:34:00 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2A3976EF59; Mon, 12 Oct 2020 20:34:00 +0000 (UTC) From: Paolo Bonzini To: qemu-devel@nongnu.org Subject: [PULL 33/38] device-core: use atomic_set on .realized property Date: Mon, 12 Oct 2020 16:33:38 -0400 Message-Id: <20201012203343.1105018-34-pbonzini@redhat.com> In-Reply-To: <20201012203343.1105018-1-pbonzini@redhat.com> References: <20201012203343.1105018-1-pbonzini@redhat.com> 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=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=63.128.21.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/12 16:33:53 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: Stefan Hajnoczi , Maxim Levitsky Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Maxim Levitsky Some code might race with placement of new devices on a bus. We currently first place a (unrealized) device on the bus and then realize it. As a workaround, users that scan the child device list, can check the realized property to see if it is safe to access such a device. Use an atomic write here too to aid with this. A separate discussion is what to do with devices that are unrealized: It looks like for this case we only call the hotplug handler's unplug callback and its up to it to unrealize the device. An atomic operation doesn't cause harm for this code path though. Signed-off-by: Maxim Levitsky Reviewed-by: Stefan Hajnoczi Message-Id: <20200913160259.32145-6-mlevitsk@redhat.com> Signed-off-by: Paolo Bonzini Message-Id: <20201006123904.610658-10-mlevitsk@redhat.com> Signed-off-by: Paolo Bonzini --- hw/core/qdev.c | 19 ++++++++++++++++++- include/hw/qdev-core.h | 2 ++ 2 files changed, 20 insertions(+), 1 deletion(-) diff --git a/hw/core/qdev.c b/hw/core/qdev.c index 59e5e710b7..fc4daa36fa 100644 --- a/hw/core/qdev.c +++ b/hw/core/qdev.c @@ -946,7 +946,25 @@ static void device_set_realized(Object *obj, bool value, Error **errp) } } + qatomic_store_release(&dev->realized, value); + } else if (!value && dev->realized) { + + /* + * Change the value so that any concurrent users are aware + * that the device is going to be unrealized + * + * TODO: change .realized property to enum that states + * each phase of the device realization/unrealization + */ + + qatomic_set(&dev->realized, value); + /* + * Ensure that concurrent users see this update prior to + * any other changes done by unrealize. + */ + smp_wmb(); + QLIST_FOREACH(bus, &dev->child_bus, sibling) { qbus_unrealize(bus); } @@ -961,7 +979,6 @@ static void device_set_realized(Object *obj, bool value, Error **errp) } assert(local_err == NULL); - dev->realized = value; return; child_realize_fail: diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h index 2c6307e3ed..868973319e 100644 --- a/include/hw/qdev-core.h +++ b/include/hw/qdev-core.h @@ -163,6 +163,8 @@ struct NamedClockList { /** * DeviceState: * @realized: Indicates whether the device has been fully constructed. + * When accessed outsize big qemu lock, must be accessed with + * atomic_load_acquire() * @reset: ResettableState for the device; handled by Resettable interface. * * This structure should not be accessed directly. We declare it here