Re: [RFC PATCH 3/3] tty: serial: fsl_lpuart: fix possible console deadlock

[Michael Walle <michael@xxxxxxxx>]

Am 2020-03-25 13:21, schrieb Leonard Crestez:
> 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@xxxxxxx>
> > Signed-off-by: Michael Walle <michael@xxxxxxxx>
>
> 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.

Yeah, it just triggers because there is now a print by default (if DMA 
is
not available) thus this RFC doesn't contain the Fixes: tag.

> 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.

TBH I don't want to refactor the whole driver. All I wanted to do was to
add LS1028A support to this driver which already resulted in a 7 patches
series with various other bugfixes. Could NXP take this over? I could
certainly do rewiews/testing on my board, though.

> 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@xxxxxxx is checked by a lot of people.

It would be good to have N: lpuart (or fsl_lpuart?) in the
corresponding entry in MAINTAINERS, so it will automatically added.
I'll try to remember for the next patches though.

-michael
> > ---
> >   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;