linux-kernel - Re: [PATCH 3.18 049/124] tty/serial: atmel: fix race condition (TX+DMA)

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Date:   Thu, 20 Apr 2017 15:37:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Richard Genoud <richard.genoud@...il.com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Nicolas Ferre <nicolas.ferre@...rochip.com>
Subject: Re: [PATCH 3.18 049/124] tty/serial: atmel: fix race condition
 (TX+DMA)

On Thu, Apr 20, 2017 at 09:46:03AM +0200, Richard Genoud wrote:
> On 20/04/2017 08:35, Greg Kroah-Hartman wrote:
> > 3.18-stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Richard Genoud <richard.genoud@...il.com>
> > 
> > commit 31ca2c63fdc0aee725cbd4f207c1256f5deaabde upstream.
> > 
> > If uart_flush_buffer() is called between atmel_tx_dma() and
> > atmel_complete_tx_dma(), the circular buffer has been cleared, but not
> > atmel_port->tx_len.
> > That leads to a circular buffer overflow (dumping (UART_XMIT_SIZE -
> > atmel_port->tx_len) bytes).
> > 
> > Tested-by: Nicolas Ferre <nicolas.ferre@...rochip.com>
> > Signed-off-by: Richard Genoud <richard.genoud@...il.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > 
> > ---
> >  drivers/tty/serial/atmel_serial.c |    5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > --- a/drivers/tty/serial/atmel_serial.c
> > +++ b/drivers/tty/serial/atmel_serial.c
> > @@ -1867,6 +1867,11 @@ static void atmel_flush_buffer(struct ua
> >  		UART_PUT_TCR(port, 0);
> >  		atmel_port->pdc_tx.ofs = 0;
> >  	}
> > +	/*
> > +	 * in uart_flush_buffer(), the xmit circular buffer has just
> > +	 * been cleared, so we have to reset tx_len accordingly.
> > +	 */
> > +	atmel_port->tx_len = 0;
> >  }
> >  
> >  /*
> > 
> > 
> Hi,
> This won't compile on 3.18 kernel since ->tx_len doesn't exist yet.
> 
> Here is the backported version of this patch:
> Thanks !
> ======================
> 
> commit 31ca2c63fdc0aee725cbd4f207c1256f5deaabde upstream.
> 
> If uart_flush_buffer() is called between atmel_tx_dma() and
> atmel_complete_tx_dma(), the circular buffer has been cleared, but not
> its length.
> That leads to a circular buffer overflow (dumping (UART_XMIT_SIZE -
> sg_dma_len(&atmel_port->sg_tx)) bytes).
> 
> Signed-off-by: Richard Genoud <richard.genoud@...il.com>
> ---
>  drivers/tty/serial/atmel_serial.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index daaed7c79e4f..a10c778be2ad 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -1867,6 +1867,11 @@ static void atmel_flush_buffer(struct uart_port *port)
>  		UART_PUT_TCR(port, 0);
>  		atmel_port->pdc_tx.ofs = 0;
>  	}
> +	/*
> +	 * in uart_flush_buffer(), the xmit circular buffer has just
> +	 * been cleared, so we have to reset its length accordingly.
> +	 */
> +	sg_dma_len(&atmel_port->sg_tx) = 0;

Thanks for the fix, now updated.

greg k-h