Re: Experiences with cvs runtime

[Martin Hunt <hunt at redhat dot com>]

On Wed, 2005-04-27 at 15:45 -0400, Ananth N Mavinakayanahalli wrote:
> Hi,
> 
> I was trying to use the probes in the runtime cvs to see if they can be
> used to test the kprobes scalability patch prototype. I ran into a few
> problems when trying to use kprobe_where_func.c.
> 
> This test was carried out on a system that was running a preempt enabled
> smp kernel (though the machine itself was uni processor). Digging around
> a bit, I see that:
> 
> - many runtime (and one relayfs) files use smp_processor_id() without
> disabling preemption

Which caused a problem when you used printk() within a probe, I assume.
We should probably disable preemption during all probes. Unless the
script compiler can guarantee that scripts won't call something that
tries to reschedule during a probe.

> - the stp script assumes that relayfs is built in as a kernel module,
> while it can be configured tristate (<*>, <M>, <>).

Do you have a suggested fix for that?  Offhand I can't think how to test
if relayfs is in a kernel from a script. "grep relayfs /proc/kallsyms"
works but is /proc/kallsyms always present now? 

> I think any code that touches the kernel needs to be tested for all 
> configurations: uni, smp, smp with preemption enabled etc.

Yes. 

Martin