Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753265AbcLBSOY (ORCPT ); Fri, 2 Dec 2016 13:14:24 -0500 Received: from mail.kmu-office.ch ([178.209.48.109]:50840 "EHLO mail.kmu-office.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751591AbcLBSOW (ORCPT ); Fri, 2 Dec 2016 13:14:22 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Date: Fri, 02 Dec 2016 10:05:36 -0800 From: Stefan Agner To: Nikita Yushchenko Cc: Greg Kroah-Hartman , Jiri Slaby , Bhuvanchandra DV , Wei Yongjun , Aaron Brice , Nicolae Rosia , linux-serial@vger.kernel.org, Chris Healy , linux-kernel@vger.kernel.org Subject: Re: [PATCH] tty: serial: fsl_lpuart: fix del_timer_sync() vs timer routine deadlock In-Reply-To: <1480674490-24718-1-git-send-email-nikita.yoush@cogentembedded.com> References: <1480674490-24718-1-git-send-email-nikita.yoush@cogentembedded.com> Message-ID: <77e2726b8b84c55f9109ff18dfcfbbdf@agner.ch> User-Agent: Roundcube Webmail/1.1.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2894 Lines: 84 On 2016-12-02 02:28, Nikita Yushchenko wrote: > Problem found via lockdep: > > - lpuart_set_termios() calls del_timer_sync(&sport->lpuart_timer) while > holding sport->port.lock > > - sport->lpuart_timer routine is lpuart_timer_func() that calls > lpuart_copy_rx_to_tty() that acquires same lock. > > To fix, move Rx DMA stopping out of lock, as it already is in other places > in the same file. > > While at it, also make Rx DMA start/stop code to look the same is in > other places in the same file. Yeah I saw that too, never really came around to look closer into it. Thanks for looking into it. You removed the check whether there was an old configuration, I think the idea of that was that we only resize DMA if it was configured differently before... Not sure how startup/set_termios calls are ordered. I guess in practice that shouldn't really make a difference since lpuart_dma_rx_use can't be true until after startup? One nit below. -- Stefan > > Signed-off-by: Nikita Yushchenko > --- > drivers/tty/serial/fsl_lpuart.c | 25 ++++++++++++++----------- > 1 file changed, 14 insertions(+), 11 deletions(-) > > diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c > index a1c6519837a4..81100c40f33b 100644 > --- a/drivers/tty/serial/fsl_lpuart.c > +++ b/drivers/tty/serial/fsl_lpuart.c > @@ -1407,6 +1407,18 @@ lpuart_set_termios(struct uart_port *port, > struct ktermios *termios, > /* ask the core to calculate the divisor */ > baud = uart_get_baud_rate(port, termios, old, 50, port->uartclk / 16); > > + /* > + * Need to update the Ring buffer length according to the selected > + * baud rate and restart Rx DMA path. > + * > + * Since timer function acqures sport->port.lock, need to stop before > + * acquring same lock because otherwise del_timer_sync() can deadlock. > + */ > + if (sport->lpuart_dma_rx_use) { > + del_timer_sync(&sport->lpuart_timer); > + lpuart_dma_rx_free(&sport->port); > + } > + > spin_lock_irqsave(&sport->port.lock, flags); > > sport->port.read_status_mask = 0; > @@ -1456,17 +1468,8 @@ lpuart_set_termios(struct uart_port *port, > struct ktermios *termios, > /* restore control register */ > writeb(old_cr2, sport->port.membase + UARTCR2); > > - /* > - * If new baud rate is set, we will also need to update the Ring buffer > - * length according to the selected baud rate and restart Rx DMA path. > - */ > - if (old) { > - if (sport->lpuart_dma_rx_use) { > - del_timer_sync(&sport->lpuart_timer); > - lpuart_dma_rx_free(&sport->port); > - } > - > - if (sport->dma_rx_chan && !lpuart_start_rx_dma(sport)) { > + if (sport->lpuart_dma_rx_use) { > + if (!lpuart_start_rx_dma(sport)) { > sport->lpuart_dma_rx_use = true; No need to set to true here, it is guaranteed to be true at this point. > rx_dma_timer_init(sport); > } else {