Re: [PATCHv5 05/17] tty: don't allow ldisc dcd_change() after ldischalt

[Alan Cox]

> Didn't know that current design is crap. :)

It's based on the old big kernel lock and it has lots of horrors when
used from interrupt paths as a result. A big chunk of it can in time I
think move to just having a per tty ldisc lock that covers all changes
etc, but we aren't there yet.

> Ok, I think I'll add a new waitqueue and a new bit (TTY_LDISC_NOREF)

We've got the wait queue already

My first guess would be something like

static struct tty_ldisc *tty_ldisc_irqget(struct tty_struct *tty)
{
        unsigned long flags;
        struct tty_ldisc *ld;
   
        spin_lock_irqsave(&tty_ldisc_lock, flags);
        ld = NULL;
        if (test_bit(TTY_LDISC, &tty->flags)) {
                ld = get_ldisc(tty->ldisc);
		WARN_ON(test_and_set_bit(TTY_LDISC_IRQ, &tty->flags));
	}
        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
        return ld;
}

static struct tty_ldisc *tty_ldisc_irqput(struct tty_ldisc *ld)
{
	clear_bit(TTY_LDISC_IRQ, &tty->flags);
	tty_ldisc_put(ld);
}

(and I think you can then wait on tty_ldisc_idle for the flag to go clear
after clearing TTY_LDISC)

It might be better to make it a count of course in case there are later
multiple users of this ?

Alan

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/