Re: [PATCH] kprobes for s390 architecture

Jan Glauber
2006-06-22T11:28:24Z

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

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