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

Alexander Gordeev
2010-12-15T16:13:52Z

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Hi,

Very sorry for the long delay.

В Thu, 25 Nov 2010 14:03:54 +0000
Alan Cox <alan@lxorguk.ukuu.org.uk> пишет:

> > 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 ?

I've just checked the code from v2.6.37 release candidates and found
that the problem is already completely fixed there with the revoking of
tty_ldisc_idle and tty_ldisc_wait_idle() in 100eeae2. :)

Sorry for the fuzz. The discussed patched is not needed any more and
will be dropped.

--
Alexander

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