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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1A3FFC433EF for ; Thu, 25 Nov 2021 20:04:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1356853AbhKYUHQ convert rfc822-to-8bit (ORCPT ); Thu, 25 Nov 2021 15:07:16 -0500 Received: from coyote.holtmann.net ([212.227.132.17]:55339 "EHLO mail.holtmann.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1356906AbhKYUFP (ORCPT ); Thu, 25 Nov 2021 15:05:15 -0500 Received: from smtpclient.apple (p5b3d2e91.dip0.t-ipconnect.de [91.61.46.145]) by mail.holtmann.org (Postfix) with ESMTPSA id 34E96CECC6; Thu, 25 Nov 2021 21:02:02 +0100 (CET) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 15.0 \(3693.20.0.1.32\)) Subject: Re: [PATCH] Bluetooth: virtio_bt: fix device removal From: Marcel Holtmann In-Reply-To: <20211125174200.133230-1-mst@redhat.com> Date: Thu, 25 Nov 2021 21:02:01 +0100 Cc: Linux Kernel Mailing List , Johan Hedberg , Luiz Augusto von Dentz , linux-bluetooth@vger.kernel.org, virtualization@lists.linux-foundation.org Content-Transfer-Encoding: 8BIT Message-Id: References: <20211125174200.133230-1-mst@redhat.com> To: "Michael S. Tsirkin" X-Mailer: Apple Mail (2.3693.20.0.1.32) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Michael, > Device removal is clearly out of virtio spec: it attempts to remove > unused buffers from a VQ before invoking device reset. To fix, make > open/close NOPs and do all cleanup/setup in probe/remove. so the virtbt_{open,close} as NOP is not really what a driver is suppose to be doing. These are transport enable/disable callbacks from the BT Core towards the driver. It maps to a device being enabled/disabled by something like bluetoothd for example. So if disabled, I expect that no resources/queues are in use. Maybe I misunderstand the virtio spec in that regard, but I would like to keep this fundamental concept of a Bluetooth driver. It does work with all other transports like USB, SDIO, UART etc. > The cost here is a single skb wasted on an unused bt device - which > seems modest. There should be no buffer used if the device is powered off. We also don’t have any USB URBs in-flight if the transport is not active. > NB: with this fix in place driver still suffers from a race condition if > an interrupt triggers while device is being reset. Work on a fix for > that issue is in progress. In the virtbt_close() callback we should deactivate all interrupts. Regards Marcel