[PATCH] mpx5200_uart: drop port lock across tty_flip_buffer() call

[Grant Likely]

On 7/25/07, Thomas Gleixner <tglx at linutronix.de> wrote:
> The port lock needs to be dropped across the tty_flip_buffer call, as it
> would lead to a deadlock with the spin_lock(&port->lock) in uart_start()
>
> Uncovered by lockdep / preempt-rt
>
> Signed-off-by: Thomas Gleixner <tglx at linutronix.de>

Instead of dropping the lock and reclaiming it, would it be better for
me to rework the driver to only grab the lock in the 'meat' of
mpc52xx_uart_int_rx_chars() and mpc52xx_uart_int_tx_chars()?   (As
opposed to holding the lock for the entirety of mpc52xx_uart_int())
What convention is used in other drivers?

Cheers,
g.

>
>
> Index: linux-2.6.22/drivers/serial/mpc52xx_uart.c
> ===================================================================
> --- linux-2.6.22.orig/drivers/serial/mpc52xx_uart.c     2007-07-09 01:32:17.000000000 +0200
> +++ linux-2.6.22/drivers/serial/mpc52xx_uart.c  2007-07-25 21:06:11.000000000 +0200
> @@ -501,7 +501,9 @@ mpc52xx_uart_int_rx_chars(struct uart_po
>                 }
>         }
>
> +       spin_unlock(&port->lock);
>         tty_flip_buffer_push(tty);
> +       spin_lock(&port->lock);
>
>         return in_be16(&PSC(port)->mpc52xx_psc_status) & MPC52xx_PSC_SR_RXRDY;
>  }
>
>
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-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
grant.likely at secretlab.ca
(403) 399-0195