Re: jiffies

["Binand Raj S." <binand@xxxxxxxxxxxxxxxxxxxxx>]

Arun Sharma forced the electrons to say:
> > Will the system go haywire if the uptime goes beyond this limit?
> 
> It may. Specifically if your machine has a driver, that has the
> following code:
> 
> now = jiffies;
> future = now + HZ * 2;
> 
> /* Wait for two seconds */
> while (jiffies < future) /* do nothing */;
> 
> Such code will hang for 497 days, locking up your system.

The reason I asked this question was, I downloaded the pcmcia-cs package, and
noticed this sort of thing in one of the modules it builds (specifically,
pcmcia-cs-3.1.11/clients/xirc2ps_cs.c):

static void
busy_loop(u_long len)
{
    if (in_interrupt()) {
	u_long timeout = jiffies + len;
	u_long flags;
	save_flags(flags);
	sti();
	while (timeout >= jiffies)
	    ;
	restore_flags(flags);
    } else {
	__set_current_state(TASK_UNINTERRUPTIBLE);
	schedule_timeout(len);
    }
}

Maybe they figured laptops won't have uptimes of 400+ days. :-)

> One common technique is to set jiffies to 0xffffffff - 1 hour, when you
> boot your system. A faulty driver will lock up in an hour.

How do you do that? set it in the kernel code itself and recompile?

Binand

-- 
The prompt for all occasions:
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--------------- Binand Raj S. (binand@xxxxxxxxxxxxxxxxxxxxx)