Re: [Linux-IrDA]Re: [IrDA+SMP] Lockup in handle_IRQ_event

[Florian Lohoff <flo@rfc822.org>]

On Thu, Jan 04, 2001 at 10:18:46AM +1100, Andrew Morton wrote:
> Marc ZYNGIER wrote:
> > 
> > Hi all,
> > 
> > Having just started playing with IrDA on my dual celeron (Abit "APIC
> > error..." BP6), I managed to kill it every single time (NMI watchdog
> > in handle_IRQ_event) while connecting to my mobile phone (in fact,
> > when closing the connection to the phone. even 'cat /dev/ircomm0' will
> > do...). This is perfectly repeatable.
> > 
> 
> Try this:
> 
> --- linux-2.4.0-prerelease/net/irda/irqueue.c	Tue Nov 21 20:11:22 2000
> +++ linux-akpm/net/irda/irqueue.c	Thu Jan  4 10:14:10 2001
> @@ -436,7 +436,7 @@
>  
>  	/* Release lock */
>  	if ( hashbin->hb_type & HB_GLOBAL) {
> -		spin_unlock_irq( &hashbin->hb_mutex[ bin]);
> +		spin_unlock_irqrestore( &hashbin->hb_mutex[ bin], flags);
>  
>  	} else if ( hashbin->hb_type & HB_LOCAL) {
>  		restore_flags( flags);

BTW: What i have seen in the ircomm_tty.c (2.2.18):

    647     save_flags(flags);
    648     cli();
    649 
    650     skb = self->tx_skb;
    651     self->tx_skb = NULL;
    652 
    653     restore_flags(flags);

and a lot of other places simply use "save_flags(flags); cli();
restore_flags()". Can someone enlighten me how this is supposed to work
on SMP machines ? AFAIK "cli()" only disables IRQs on the local
CPU so a different CPU could easily stumple half way as this
is definitly non atomic. Or is the tty layer protected by some
"big tty lock" ?

Flo
-- 
Florian Lohoff                  flo@rfc822.org             +49-5201-669912
     Why is it called "common sense" when nobody seems to have any?

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