linux-kernel - Re: [PATCH] serial: fix possible imx deadlock

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Message-ID: <20100315134556.GX19843@pengutronix.de>
Date:	Mon, 15 Mar 2010 14:45:57 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	John Ogness <john.ogness@...utronix.de>
Cc:	Sascha Hauer <kernel@...gutronix.de>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] serial: fix possible imx deadlock

On Mon, Mar 15, 2010 at 10:08:58AM +0100, John Ogness wrote:
> This patch fixes a possible deadlock situation with the port and timer
> locks. The calling paths for the deadlock situation are:
> 
> 1. imx_set_termios() -> LOCK(port.lock)
>       -> del_timer_sync() -> LOCK(timer.base.lock)
> 
> 2. run_timer_softirq() -> LOCK(timer.base.lock)
>       -> imx_timeout() -> LOCK(port.lock)
> 
> This patch is against 2.6.34-rc1.
> 
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> ---
>  drivers/serial/imx.c |    8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> diff -Naurp a/drivers/serial/imx.c b/drivers/serial/imx.c
> --- a/drivers/serial/imx.c	2010-03-08 19:45:44.000000000 +0100
> +++ b/drivers/serial/imx.c	2010-03-15 09:52:39.855261060 +0100
> @@ -836,6 +836,12 @@ imx_set_termios(struct uart_port *port, 
>  	baud = uart_get_baud_rate(port, termios, old, 50, port->uartclk / 16);
>  	quot = uart_get_divisor(port, baud);
>  
> +	/*
> +	 * Stop our timer. This is done with the port unlocked
> +	 * to avoid possible deadlock against the timer function.
> +	 */
> +	del_timer_sync(&sport->timer);
> +

Is this call needed here anyway? Only few drivers have it. Does anyone
have more insights on this?

Sascha

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