Re: [patch] softirq-2.4.5-B0

[Andi Kleen <ak@suse.de>]

"David S. Miller" <davem@redhat.com> writes:

>  > the attached softirq-2.4.5-B0 patch fixes this problem by calling
>  > do_softirq()  from local_bh_enable() [if the bh count is 0, to avoid
>  > recursion].
> 
> Yikes!  I do not like this fix.
> 
> I'd rather local_bh_enable() not become a more heavy primitive.
> 
> I know, in one respect it makes sense because it parallels how
> hardware interrupts work, but not this thing is a function call
> instead of a counter bump :-(
> 
> Any other ideas how to zap this?

I think the right way to fix it is to do a final atomic check for softirqs 
when the kernel is exited. To be atomic this check neededs to be done with 
interrupts off until the kernel exited. I just implemented a very similar way 
into the x86-64 kernel (which needs to turn off interrupts for kernel anyways 
for other reasons, this just extends the cli area a bit). The same atomic
check is needed for race free check of need_schedule (which is still racy
on plain i386). 

-Andi