linux-kernel - Re: [PATCH 8/8] serial: tegra: Correct error handling on DMA setup

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Date:	Tue, 12 May 2015 17:39:31 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Laxman Dewangan <ldewangan@...dia.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 8/8] serial: tegra: Correct error handling on DMA setup

On Tue, May 5, 2015 at 11:17 PM, Jon Hunter <jonathanh@...dia.com> wrote:
> Function tegra_uart_dma_channel_allocate() does not check that
> dma_map_single() mapped the DMA buffer correctly. Add a check for this
> and appropriate error handling.
>
> Furthermore, if dmaengine_slave_config() (called by
> tegra_uart_dma_channel_allocate()) fails, then memory allocated/mapped
> is not freed/unmapped. Therefore, call tegra_uart_dma_channel_free()
> instead of just dma_release_channel() if  dmaengine_slave_config() fails.
>
> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
> ---
>  drivers/tty/serial/serial-tegra.c | 51 +++++++++++++++++++++------------------
>  1 file changed, 28 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/tty/serial/serial-tegra.c b/drivers/tty/serial/serial-tegra.c
> index 96378da9aefc..3b63f103f0c9 100644
> --- a/drivers/tty/serial/serial-tegra.c
> +++ b/drivers/tty/serial/serial-tegra.c
> @@ -949,6 +949,28 @@ static int tegra_uart_hw_init(struct tegra_uart_port *tup)
>         return 0;
>  }
>
> +static void tegra_uart_dma_channel_free(struct tegra_uart_port *tup,
> +               bool dma_to_memory)
> +{
> +       if (dma_to_memory) {
> +               dmaengine_terminate_all(tup->rx_dma_chan);
> +               dma_release_channel(tup->rx_dma_chan);
> +               dma_free_coherent(tup->uport.dev, TEGRA_UART_RX_DMA_BUFFER_SIZE,
> +                               tup->rx_dma_buf_virt, tup->rx_dma_buf_phys);
> +               tup->rx_dma_chan = NULL;
> +               tup->rx_dma_buf_phys = 0;
> +               tup->rx_dma_buf_virt = NULL;
> +       } else {
> +               dmaengine_terminate_all(tup->tx_dma_chan);
> +               dma_release_channel(tup->tx_dma_chan);
> +               dma_unmap_single(tup->uport.dev, tup->tx_dma_buf_phys,
> +                       UART_XMIT_SIZE, DMA_TO_DEVICE);
> +               tup->tx_dma_chan = NULL;
> +               tup->tx_dma_buf_phys = 0;
> +               tup->tx_dma_buf_virt = NULL;
> +       }
> +}
> +
>  static int tegra_uart_dma_channel_allocate(struct tegra_uart_port *tup,
>                         bool dma_to_memory)
>  {
> @@ -981,6 +1003,11 @@ static int tegra_uart_dma_channel_allocate(struct tegra_uart_port *tup,
>                 dma_phys = dma_map_single(tup->uport.dev,
>                         tup->uport.state->xmit.buf, UART_XMIT_SIZE,
>                         DMA_TO_DEVICE);
> +               if (dma_mapping_error(tup->uport.dev, dma_phys)) {
> +                       dev_err(tup->uport.dev, "dma_map_single tx failed\n");
> +                       dma_release_channel(dma_chan);
> +                       return -ENOMEM;

Is -ENOMEM the error code we want to return here?

IIUC dma_buf will be leaked if an error occurs here because it has not
been assigned to your structure and will therefore be ignored when
tegra_uart_dma_channel_free() is called.

Since we have a "scrub" label at the end of this function, I think I'd
also prefer if this block and the one before could jump to error
labels as well for consistency.

Otherwise, pretty nice series, comprehensive and easy to read.
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