Re: [PATCH] kprobes for s390 architecture

[Jan Glauber <jan.glauber@de.ibm.com>]

On Wed, 2006-06-21 at 10:34 -0700, Mike Grundy wrote:
> On Wed, Jun 21, 2006 at 06:38:40PM +0200, Martin Schwidefsky wrote:
> > You misunderstood me here. I'm not talking about storing the same piece
> > of data to memory on each processor. I'm talking about isolating all
> > other cpus so that the initiating cpu can store the breakpoint to memory
> > without running into the danger that another cpu is trying to execute it
> > at the same time. But probably the store should be atomic in regard to
> > instruction fetching on the other cpus. It is only two bytes and it
> > should be aligned.
> 
> So maybe something like this:
> 
> void smp_replace_instruction(void *info) {
>         struct ins_replace_args *parms;
>         parms = (struct ins_replace_args *) info;
>         *parms->addr = *parms->insn
> }
> 
> void __kprobes arch_arm_kprobe(struct kprobe *p)
> {
>         struct ins_replace_args parms;
>         parms.addr = p->addr;
>         parms.insn = BREAKPOINT_INSTRUCTION
> 
>         preempt_disable();
>         smp_call_function(smp_replace_instruction, &parms, 0, 1);
>         preempt_enable();
> }

Preemption disabling is not necessary around smp_call_function(), since
smp_call_function() takes a spin lock. But smp_call_function() is wrong
here, it calls the code on all other CPUs but not on our own. Please use
on_each_cpu() instead.

Jan

---
Jan Glauber
IBM Linux Technology Center
Linux on zSeries Development, Boeblingen