Re: [PATCH] kprobes for s390 architecture

[Mike Grundy <grundym at us dot ibm dot com>]

On Wed, Jun 28, 2006 at 07:58:57AM +0200, Heiko Carstens wrote:
> On Tue, Jun 27, 2006 at 05:23:09PM +0200, Martin Schwidefsky wrote:
> > On Sat, 2006-06-24 at 13:36 +0200, Heiko Carstens wrote:
> > > Just do a compare and swap operation on the instruction you want to replace,
> > > then do an smp_call_function() with the wait parameter set to 1 and passing
> > > a pointer to a function that does nothing but return.
> > Not good enough. An instruction can be fetched multiple times for a
> > single execution (see the other mail). So you have a half executed
> > instruction, the cache line is invalidated, a new instruction is written
> > and the cache line is recreated to finished the half executed
> > instruction. That can easiliy happen on millicoded instructions.
> 
> Yes, looks like I was too optimistic. Seems like we really have to go for
> stop_machine_run() unless somebody comes up with a better idea...

ok, I tried, but my "better ideas" made things worse. stop_machine_run() wins:

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        unsigned long status = kcb->kprobe_status;
        struct ins_replace_args args;

        args.ptr = p->addr;
        args.old = p->opcode;
        args.new = BREAKPOINT_INSTRUCTION;

        kcb->kprobe_status = KPROBE_SWAP_INST;
        stop_machine_run(swap_instruction, &args, NR_CPUS);
        kcb->kprobe_status = status;
}

It works, and I guess at this point is the only way to do it. I'll send out a 
full patch with this and the other cleanups later.

Mike