linux-kernel - Re: [PATCH 3.4 stable][PATCH] pch_uart: fix a deadlock when pch

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Date:	Fri, 28 Jun 2013 15:54:03 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Yijing Wang <wangyijing@...wei.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>, Liang Li <liang.li@...driver.com>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH 3.4 stable][PATCH] pch_uart: fix a deadlock when pch_uart
 as console

Hi Greg,
   I'm very sorry this email format problems, please drop this one,
I will resend a correct email to describe this patch later.

Thanks!
Yijing.

On 2013/6/28 11:10, Yijing Wang wrote:
> From: Liang Li <liang.li@...driver.com>
> 
> commit 384e301e3519599b000c1a2ecd938b533fc15d85 upstream
> 
> When we use pch_uart as system console like 'console=ttyPCH0,115200',
> then 'send break' to it. We'll encounter the deadlock on a cpu/core,
> with interrupts disabled on the core. When we happen to have all irqs
> affinity to cpu0 then the deadlock on cpu0 actually deadlock whole
> system.
> 
> In pch_uart_interrupt, we have spin_lock_irqsave(&priv->lock, flags)
> then call pch_uart_err_ir when break is received. Then the call to
> dev_err would actually call to pch_console_write then we'll run into
> another spin_lock(&priv->lock), with interrupts disabled.
> 
> So in the call sequence lead by pch_uart_interrupt, we should be
> carefully to call functions that will 'print message to console' only
> in case the uart port is not being used as serial console.
> 
> Signed-off-by: Liang Li <liang.li@...driver.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Yijing Wang <wangyijing@...wei.com>
> Cc: stable@...r.kernel.org
> ---
>  drivers/tty/serial/pch_uart.c |   29 ++++++++++++++++++++++-------
>  1 files changed, 22 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
> index 8b40a1f..10e1a95 100644
> --- a/drivers/tty/serial/pch_uart.c
> +++ b/drivers/tty/serial/pch_uart.c
> @@ -1024,22 +1024,37 @@ static unsigned int dma_handle_tx(struct eg20t_port *priv)
>  static void pch_uart_err_ir(struct eg20t_port *priv, unsigned int lsr)
>  {
>  	u8 fcr = ioread8(priv->membase + UART_FCR);
> +	struct uart_port *port = &priv->port;
> +	struct tty_struct *tty = tty_port_tty_get(&port->state->port);
> +	char   *error_msg[5] = {};
> +	int    i = 0;
>  
>  	/* Reset FIFO */
>  	fcr |= UART_FCR_CLEAR_RCVR;
>  	iowrite8(fcr, priv->membase + UART_FCR);
>  
>  	if (lsr & PCH_UART_LSR_ERR)
> -		dev_err(&priv->pdev->dev, "Error data in FIFO\n");
> +		error_msg[i++] = "Error data in FIFO\n";
> +
> +	if (lsr & UART_LSR_FE) {
> +		port->icount.frame++;
> +		error_msg[i++] = "  Framing Error\n";
> +	}
>  
> -	if (lsr & UART_LSR_FE)
> -		dev_err(&priv->pdev->dev, "Framing Error\n");
> +	if (lsr & UART_LSR_PE) {
> +		port->icount.parity++;
> +		error_msg[i++] = "  Parity Error\n";
> +	}
>  
> -	if (lsr & UART_LSR_PE)
> -		dev_err(&priv->pdev->dev, "Parity Error\n");
> +	if (lsr & UART_LSR_OE) {
> +		port->icount.overrun++;
> +		error_msg[i++] = "  Overrun Error\n";
> +	}
>  
> -	if (lsr & UART_LSR_OE)
> -		dev_err(&priv->pdev->dev, "Overrun Error\n");
> +	if (tty == NULL) {
> +		for (i = 0; error_msg[i] != NULL; i++)
> +			dev_err(&priv->pdev->dev, error_msg[i]);
> +	}
>  }
>  
>  static irqreturn_t pch_uart_interrupt(int irq, void *dev_id)
> 


-- 
Thanks!
Yijing

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