Pavel Machek wrote:
> 
> > >
> > > I've seen similar bugs. If you hook something on schedule_tq and
> > forget
> > > to set current->need_resched, this is exactly what you get.
> > >
> > I'm running with a patch that printk's if cpu_idle() is called while a
> > softirq is pending.
> > If I access the floppy on my K6/200 every track triggers the check, and
> > sometimes the console blanking code triggers it.
> 
> Seems floppy and console is buggy, then.
>

No. The softirq implementation is buggy.
I can trigger the problem with the TASKLET_HI (floppy), and both net rx
and tx (ping -l)

> > What about creating a special cpu_is_idle() function that the idle
> > functions must call before sleeping?
> 
> I'd say just fix all the bugs.
>

Ok, there are 2 bugs that are (afaics) impossible to fix without
checking for pending softirq's in cpu_idle():

a)
queue_task(my_task1, tq_immediate);
mark_bh();
schedule();
;within schedule: do_softirq()
;within my_task1:
mark_bh();
; bh returns, but do_softirq won't loop
; do_softirq returns.
; schedule() clears current->need_resched
; idle thread scheduled.
--> idle can run although softirq's are pending

I assume I trigger this race with the floppy driver.

b)
hw interrupt
do_softirq
within the net_rx handler: another hw interrupt, additional packets are
queued
do_softirq won't loop.
returns to idle thread. --> packets delayed unnecessary.

What about the attached patch? Obviously the other idle cpu must be
converted to use the function as well.

--
	Manfred