Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752366AbcLGBvO (ORCPT ); Tue, 6 Dec 2016 20:51:14 -0500 Received: from mail.kmu-office.ch ([178.209.48.109]:49713 "EHLO mail.kmu-office.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751518AbcLGBvJ (ORCPT ); Tue, 6 Dec 2016 20:51:09 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Date: Tue, 06 Dec 2016 17:44:30 -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 v2] tty: serial: fsl_lpuart: fix del_timer_sync() vs timer routine deadlock In-Reply-To: <1480866568-15725-1-git-send-email-nikita.yoush@cogentembedded.com> References: <1480866568-15725-1-git-send-email-nikita.yoush@cogentembedded.com> Message-ID: 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: 3107 Lines: 94 On 2016-12-04 07:49, 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. Looks good here: Tested-by: Stefan Agner > > Signed-off-by: Nikita Yushchenko > --- > Changes from v1: > - keep reallocation of Rx DMA buffer conditional on 'old' > - do not set sport->lpuart_dma_rx_use to true when it is already true > > drivers/tty/serial/fsl_lpuart.c | 35 +++++++++++++++++------------------ > 1 file changed, 17 insertions(+), 18 deletions(-) > > diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c > index a1c6519837a4..f02934ffb329 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 (old && 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; > @@ -1456,22 +1468,11 @@ 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)) { > - sport->lpuart_dma_rx_use = true; > + if (old && sport->lpuart_dma_rx_use) { > + if (!lpuart_start_rx_dma(sport)) > rx_dma_timer_init(sport); > - } else { > + else > sport->lpuart_dma_rx_use = false; > - } > } > > spin_unlock_irqrestore(&sport->port.lock, flags); > @@ -2131,12 +2132,10 @@ static int lpuart_resume(struct device *dev) > > if (sport->lpuart_dma_rx_use) { > if (sport->port.irq_wake) { > - if (!lpuart_start_rx_dma(sport)) { > - sport->lpuart_dma_rx_use = true; > + if (!lpuart_start_rx_dma(sport)) > rx_dma_timer_init(sport); > - } else { > + else > sport->lpuart_dma_rx_use = false; > - } > } > }