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

[Anton Blanchard <anton@linuxcare.com.au>]

 
> 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" ?

On SMP __cli() disables interrupts on the local cpu, cli() also grabs
the global irq lock which serialises irqs between cpus. 

Using a spinlock is much preferred if possible as grabbing the global
irq lock is expensive (and in most cases unnecessary).

Anton
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