Re: [PATCH -tip v3 7/7] kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT

[Ingo Molnar]

* Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:

> On Fri, 29 Sep 2017 09:37:55 +0200
> Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> 
> > 
> > * Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> > 
> > > On Thu, 28 Sep 2017 09:22:20 +0200
> > > Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> > > 
> > > > 
> > > > * Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> > > > 
> > > > > To enable jump optimized probe with CONFIG_PREEMPT, use
> > > > > synchronize_rcu_tasks() to wait for all tasks preempted
> > > > > on trampoline code back on track.
> > > > 
> > > > This sentence does not parse. It's missing a verb, but I'm not sure.
> > > 
> > > Hmm, how about this?
> > > 
> > > Use synchthnize_rcu_tasks() to wait for all tasks preempted
> > > on trampoline code back on track so that jump optimized probe
> > > can be enabled with CONFIG_PREEMPT.
> > 
> > What's "synchthnize"? ...
> 
> Oops, it's my typo. my XPS touch pad is really unstable...
> 
> > 
> > More seriously, I still don't understand it. What is 'back on track'?
> > 
> > Do you mean to say:
> > 
> >    We want to wait for all potentially preempted kprobes trampoline execution to 
> >    have completed. This guarantees that any freed trampoline memory is not in use
> >    by any task in the system anymore. synchronize_rcu_tasks() gives such a
> >    guarantee, so use it.
> 
> Exactly, this is correct!

Ok, great - please re-send the remaining kprobes patches that I have not applied 
yet - I'll read through the changelogs and fix any bits that might still be 
unclear.

Thanks,

	Ingo