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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 7BD56C4360F for ; Tue, 2 Apr 2019 12:38:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5225220883 for ; Tue, 2 Apr 2019 12:38:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731013AbfDBMiK (ORCPT ); Tue, 2 Apr 2019 08:38:10 -0400 Received: from mx2.suse.de ([195.135.220.15]:35170 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725959AbfDBMiJ (ORCPT ); Tue, 2 Apr 2019 08:38:09 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id EC509AE80; Tue, 2 Apr 2019 12:38:07 +0000 (UTC) Message-ID: <1554208674.6310.33.camel@suse.com> Subject: Re: [PATCH V4 1/3] USB: serial: f81232: clear overrun flag From: Oliver Neukum To: "Ji-Ze Hong (Peter Hong)" , peter_hong@fintek.com.tw, johan@kernel.org, gregkh@linuxfoundation.org Cc: "Ji-Ze Hong (Peter Hong)" , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Date: Tue, 02 Apr 2019 14:37:54 +0200 In-Reply-To: <1554182797-12815-1-git-send-email-hpeter+linux_kernel@gmail.com> References: <1554182797-12815-1-git-send-email-hpeter+linux_kernel@gmail.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.6 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Di, 2019-04-02 at 13:26 +0800, Ji-Ze Hong (Peter Hong) wrote: > The F81232 will report data and LSR with bulk like following format: > bulk-in data: [LSR(1Byte)+DATA(1Byte)][LSR(1Byte)+DATA(1Byte)]... > > LSR will auto clear frame/parity/break error flag when reading by H/W, > but overrrun will only cleared when reading LSR. So this patch add a > worker to read LSR when overrun and flush the worker on close() & > suspend(). Hi, I really hate doing this to you, but you are exchanging one race condition for another race. Exact explanation below. > @@ -315,6 +319,7 @@ static void f81232_process_read_urb(struct urb *urb) > > if (lsr & UART_LSR_OE) { > port->icount.overrun++; > + schedule_work(&priv->lsr_work); Again you schedule the work. It may run anytime. The check you put into the work item needs to go here. > +static void f81232_lsr_worker(struct work_struct *work) > +{ > + struct f81232_private *priv; > + struct usb_serial_port *port; > + struct usb_serial *serial; > + int status; > + u8 tmp; > + > + priv = container_of(work, struct f81232_private, lsr_work); > + port = priv->port; > + serial = port->serial; > + > + if (serial->suspending) { There is no locking. f81232_resume() can run here. This test if (port_priv->lsr_work_resched) { will evaluate to false > + priv->lsr_work_resched = true; > + return; > + } > + > + status = f81232_get_register(port, LINE_STATUS_REGISTER, &tmp); > + if (status) > + dev_warn(&port->dev, "read LSR failed: %d\n", status); > +} > + > static int f81232_port_probe(struct usb_serial_port *port) > { > struct f81232_private *priv; > @@ -613,6 +643,7 @@ static int f81232_port_probe(struct usb_serial_port *port) > > mutex_init(&priv->lock); > INIT_WORK(&priv->interrupt_work, f81232_interrupt_work); > + INIT_WORK(&priv->lsr_work, f81232_lsr_worker); > > usb_set_serial_port_data(port, priv); > > @@ -632,6 +663,30 @@ static int f81232_port_remove(struct usb_serial_port *port) > return 0; > } > > +static int f81232_suspend(struct usb_serial *serial, pm_message_t message) > +{ > + struct f81232_private *port_priv; > + > + port_priv = usb_get_serial_port_data(serial->port[0]); > + flush_work(&port_priv->lsr_work); Strictly speaking useless. > + > + return 0; > +} > + > +static int f81232_resume(struct usb_serial *serial) > +{ > + struct f81232_private *port_priv; > + > + port_priv = usb_get_serial_port_data(serial->port[0]); > + > + if (port_priv->lsr_work_resched) { > + port_priv->lsr_work_resched = false; Strictly speaking even that is a race, as you have no guarantee that your work queue is run before the system is suspended again. You are in a task context. There is no reason to defer action. > + schedule_work(&port_priv->lsr_work); > + } > + > + return usb_serial_generic_resume(serial); > +} Regards Oliver