Re: [PATCH] protect 'action' in show_interrupts

[Andrew Morton <akpm@digeo.com>]

Zwane Mwaikambo <zwane@linuxpower.ca> wrote:
>
> This patch protects a critical section in show_interrupts against 
> removal of 'action' during traversal of the handlers. All the 
> architectures in one swoop.

Thanks for doing this.

> ...
> --- linux-2.5.64/arch/i386/kernel/irq.c	5 Mar 2003 05:08:03 -0000	1.1.1.1
> +++ linux-2.5.64/arch/i386/kernel/irq.c	7 Mar 2003 09:04:43 -0000
>  static void register_irq_proc (unsigned int irq);
> @@ -135,6 +135,7 @@
>  {
>  	int i, j;
>  	struct irqaction * action;
> +	unsigned long flags;
>  
>  	seq_printf(p, "           ");
>  	for (j=0; j<NR_CPUS; j++)
> @@ -156,11 +157,17 @@
>  					     kstat_cpu(j).irqs[i]);
>  #endif
>  		seq_printf(p, " %14s", irq_desc[i].handler->typename);
> +		spin_lock_irqsave(&irq_desc[i].lock, flags);
> +		if (!action)
> +			goto unlock;
> +		seq_printf(p, "  %s", action->name);
 
Local variable `action' could be pointing at freed memory by now.  We need to
reload it inside the lock.  Or just hold the lock across the entire loop.