Re: your mail

Jiri Slaby
2012-02-12T12:40:54Z

On 02/12/2012 02:02 AM, Al Viro wrote:
> On Sun, Feb 12, 2012 at 01:21:10AM +0100, Richard Weinberger wrote:
>> +++ b/arch/um/drivers/line.c
>> @@ -19,19 +19,29 @@ static irqreturn_t line_interrupt(int irq, void *data)
>> {
>> struct chan *chan = data;
>> struct line *line = chan->line;
>> + struct tty_struct *tty;
>> +
>> + if (line) {
>> + tty = tty_port_tty_get(&line->port);
>> + chan_interrupt(&line->chan_list, &line->task, tty, irq);
>> + tty_kref_put(tty);
>> + }
>>
>> - if (line)
>> - chan_interrupt(&line->chan_list, &line->task, line->tty, irq);
>> return IRQ_HANDLED;
>> }
>
> Is tty_kref_put() safe in interrupt? Here it seems to be OK, but in other
> callers... More or less at random: drivers/tty/serial/lantiq.c has it
> called from lqasc_rx_int(). It seems to be possible to have it end up
> calling ->ops->shutdown() and in this case that'd be lqasc_shutdown().
> Which does a bunch of free_irq(), including the ->rx_irq, i.e. the one
> we have it called from. Alan?

I'm not Alan, but will reply anyway. Yes, it is safe (unless the driver
does something tricky). In the driver you mention, this is uart_ops,
called from tty_port_operations' ->shutdown. And that's a different from
tty_operations' ->shutdown.

Yes, there are:
* tty->ops
* tty_port->ops
* uart_port->ops

uart_port->ops->shutdown is supposed to tear down interrupts like in
lantiq.c. It is called from tty_port->ops->shutdown. And that one is
allowed to be called only from user context (tty->ops->close and
tty->ops->hangup).

thanks,
--
js
suse labs