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SubjectRe: [RFC PATCH 3/3] tty: serial: fsl_lpuart: fix possible console deadlock
Date
On 2020-03-24 8:48 PM, Michael Walle wrote:
> If the kernel console output is on this console any
> dev_{err,warn,info}() may result in a deadlock if the sport->port.lock
> spinlock is already held. This is because the _console_write() try to
> aquire this lock, too. Remove any error messages where the spinlock is
> taken or print after the lock is released.
>
> Reported-by: Leonard Crestez <leonard.crestez@nxp.com>
> Signed-off-by: Michael Walle <michael@walle.cc>

It seems that this was an issue even before commit 159381df1442 ("tty:
serial: fsl_lpuart: fix DMA operation when using IOMMU") but these error
prints never triggered.

Would it be possible to move all the dma alloc/config/prep outside the
serial port lock? As it stands this still calls into dmaengine coode and
that might decide to print as well.

Really I don't think the lock needs to protect more than bits like
TDMAE/RDMAE.

BTW: You should add more people in CC for reviews, for example
linux-imx@nxp.com is checked by a lot of people.

> ---
> drivers/tty/serial/fsl_lpuart.c | 35 +++++++--------------------------
> 1 file changed, 7 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
> index bbba298b68a4..0910308b38b1 100644
> --- a/drivers/tty/serial/fsl_lpuart.c
> +++ b/drivers/tty/serial/fsl_lpuart.c
> @@ -420,7 +420,6 @@ static void lpuart_dma_tx(struct lpuart_port *sport)
> {
> struct circ_buf *xmit = &sport->port.state->xmit;
> struct scatterlist *sgl = sport->tx_sgl;
> - struct device *dev = sport->port.dev;
> struct dma_chan *chan = sport->dma_tx_chan;
> int ret;
>
> @@ -442,10 +441,8 @@ static void lpuart_dma_tx(struct lpuart_port *sport)
>
> ret = dma_map_sg(chan->device->dev, sgl, sport->dma_tx_nents,
> DMA_TO_DEVICE);
> - if (!ret) {
> - dev_err(dev, "DMA mapping error for TX.\n");
> + if (!ret)
> return;
> - }
>
> sport->dma_tx_desc = dmaengine_prep_slave_sg(chan, sgl,
> ret, DMA_MEM_TO_DEV,
> @@ -453,7 +450,6 @@ static void lpuart_dma_tx(struct lpuart_port *sport)
> if (!sport->dma_tx_desc) {
> dma_unmap_sg(chan->device->dev, sgl, sport->dma_tx_nents,
> DMA_TO_DEVICE);
> - dev_err(dev, "Cannot prepare TX slave DMA!\n");
> return;
> }
>
> @@ -520,21 +516,12 @@ static int lpuart_dma_tx_request(struct uart_port *port)
> struct lpuart_port *sport = container_of(port,
> struct lpuart_port, port);
> struct dma_slave_config dma_tx_sconfig = {};
> - int ret;
>
> dma_tx_sconfig.dst_addr = lpuart_dma_datareg_addr(sport);
> dma_tx_sconfig.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> dma_tx_sconfig.dst_maxburst = 1;
> dma_tx_sconfig.direction = DMA_MEM_TO_DEV;
> - ret = dmaengine_slave_config(sport->dma_tx_chan, &dma_tx_sconfig);
> -
> - if (ret) {
> - dev_err(sport->port.dev,
> - "DMA slave config failed, err = %d\n", ret);
> - return ret;
> - }
> -
> - return 0;
> + return dmaengine_slave_config(sport->dma_tx_chan, &dma_tx_sconfig);
> }
>
> static bool lpuart_is_32(struct lpuart_port *sport)
> @@ -1074,8 +1061,8 @@ static void lpuart_copy_rx_to_tty(struct lpuart_port *sport)
>
> dmastat = dmaengine_tx_status(chan, sport->dma_rx_cookie, &state);
> if (dmastat == DMA_ERROR) {
> - dev_err(sport->port.dev, "Rx DMA transfer failed!\n");
> spin_unlock_irqrestore(&sport->port.lock, flags);
> + dev_err(sport->port.dev, "Rx DMA transfer failed!\n");
> return;
> }
>
> @@ -1179,23 +1166,17 @@ static inline int lpuart_start_rx_dma(struct lpuart_port *sport)
> sg_init_one(&sport->rx_sgl, ring->buf, sport->rx_dma_rng_buf_len);
> nent = dma_map_sg(chan->device->dev, &sport->rx_sgl, 1,
> DMA_FROM_DEVICE);
> -
> - if (!nent) {
> - dev_err(sport->port.dev, "DMA Rx mapping error\n");
> + if (!nent)
> return -EINVAL;
> - }
>
> dma_rx_sconfig.src_addr = lpuart_dma_datareg_addr(sport);
> dma_rx_sconfig.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> dma_rx_sconfig.src_maxburst = 1;
> dma_rx_sconfig.direction = DMA_DEV_TO_MEM;
> - ret = dmaengine_slave_config(chan, &dma_rx_sconfig);
>
> - if (ret < 0) {
> - dev_err(sport->port.dev,
> - "DMA Rx slave config failed, err = %d\n", ret);
> + ret = dmaengine_slave_config(chan, &dma_rx_sconfig);
> + if (ret < 0)
> return ret;
> - }
>
> sport->dma_rx_desc = dmaengine_prep_dma_cyclic(chan,
> sg_dma_address(&sport->rx_sgl),
> @@ -1203,10 +1184,8 @@ static inline int lpuart_start_rx_dma(struct lpuart_port *sport)
> sport->rx_sgl.length / 2,
> DMA_DEV_TO_MEM,
> DMA_PREP_INTERRUPT);
> - if (!sport->dma_rx_desc) {
> - dev_err(sport->port.dev, "Cannot prepare cyclic DMA\n");
> + if (!sport->dma_rx_desc)
> return -EFAULT;
> - }
>
> sport->dma_rx_desc->callback = lpuart_dma_rx_complete;
> sport->dma_rx_desc->callback_param = sport;
>


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