linux-kernel - Re: [PATCH] tty: serial: men_z135_uart.c: Fix race between IRQ and set

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Date:	Mon, 03 Aug 2015 11:31:08 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Johannes Thumshirn <jthumshirn@...e.de>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Andreas Werner <andreas.werner@....de>
Subject: Re: [PATCH] tty: serial: men_z135_uart.c: Fix race between IRQ and
 set_termios()

Hi Johannes,

On 08/03/2015 09:58 AM, Johannes Thumshirn wrote:
> Fix panic caused by a race between men_z135_intr() and men_z135_set_termios().
> 
> men_z135_intr() and men_z135_set_termios() both hold the struct uart_port::lock
> spinlock, but men_z135_intr() does a spin_lock_irqsave() and
> men_z135_set_termios() does a normal spin_lock(), which can lead to a deadlock
> when an interrupt is called while the lock is being helt by
> men_z135_set_termios().


The irq handler can and should use normal spin_lock()/unlock().

The set_termios() method should used spin_lock_irq(); there's no need to save the
interrupt state because that method will never be called from interrupt context.

So the 'flags' local can be dropped from the patch.

Also, the port lock is already initialized in uart_add_one_port() and should
not be initialized by the probe() function.

Regards,
Peter Hurley

> This was discovered using a insmod, hardware looppback send/receive, rmmod
> stress test.
> 
> Signed-off-by: Johannes Thumshirn <jthumshirn@...e.de>
> Cc: Andreas Werner <andreas.werner@....de>
> ---
>  drivers/tty/serial/men_z135_uart.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/men_z135_uart.c b/drivers/tty/serial/men_z135_uart.c
> index 35c5550..d020435 100644
> --- a/drivers/tty/serial/men_z135_uart.c
> +++ b/drivers/tty/serial/men_z135_uart.c
> @@ -656,6 +656,7 @@ static void men_z135_set_termios(struct uart_port *port,
>  				struct ktermios *old)
>  {
>  	struct men_z135_port *uart = to_men_z135(port);
> +	unsigned long flags;
>  	unsigned int baud;
>  	u32 conf_reg;
>  	u32 bd_reg;
> @@ -717,7 +718,7 @@ static void men_z135_set_termios(struct uart_port *port,
>  
>  	baud = uart_get_baud_rate(port, termios, old, 0, uart_freq / 16);
>  
> -	spin_lock(&port->lock);
> +	spin_lock_irqsave(&port->lock, flags);
>  	if (tty_termios_baud_rate(termios))
>  		tty_termios_encode_baud_rate(termios, baud, baud);
>  
> @@ -725,7 +726,7 @@ static void men_z135_set_termios(struct uart_port *port,
>  	iowrite32(bd_reg, port->membase + MEN_Z135_BAUD_REG);
>  
>  	uart_update_timeout(port, termios->c_cflag, baud);
> -	spin_unlock(&port->lock);
> +	spin_unlock_irqrestore(&port->lock, flags);
>  }
>  
>  static const char *men_z135_type(struct uart_port *port)
> 

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