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

From Ingo Molnar <mingo@kernel.org>
Newsgroups linux.kernel
Subject Re: [PATCH -tip v3 7/7] kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT
Date 2017-09-29 09:40 +0200
Message-ID <uuY3T-3eu-1@gated-at.bofh.it> (permalink)
References <urntU-3th-5@gated-at.bofh.it> <urnDA-3YD-3@gated-at.bofh.it> <uuBqG-5Tq-9@gated-at.bofh.it> <uuXUe-3aS-29@gated-at.bofh.it>
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* Masami Hiramatsu <mhiramat@kernel.org> wrote:

> On Thu, 28 Sep 2017 09:22:20 +0200
> Ingo Molnar <mingo@kernel.org> wrote:
> 
> > 
> > * Masami Hiramatsu <mhiramat@kernel.org> 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"? ...

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.

or something else?

Thanks,

	Ingo

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Re: [PATCH -tip v3 7/7] kprobes: Use synchronize_rcu_tasks() for  optprobe with CONFIG_PREEMPT Ingo Molnar <mingo@kernel.org> - 2017-09-28 09:30 +0200
  Re: [PATCH -tip v3 7/7] kprobes: Use synchronize_rcu_tasks() for  optprobe with CONFIG_PREEMPT Masami Hiramatsu <mhiramat@kernel.org> - 2017-09-29 09:30 +0200
    Re: [PATCH -tip v3 7/7] kprobes: Use synchronize_rcu_tasks() for  optprobe with CONFIG_PREEMPT Ingo Molnar <mingo@kernel.org> - 2017-09-29 09:40 +0200
      Re: [PATCH -tip v3 7/7] kprobes: Use synchronize_rcu_tasks() for  optprobe with CONFIG_PREEMPT Masami Hiramatsu <mhiramat@kernel.org> - 2017-09-29 16:50 +0200
        Re: [PATCH -tip v3 7/7] kprobes: Use synchronize_rcu_tasks() for  optprobe with CONFIG_PREEMPT Ingo Molnar <mingo@kernel.org> - 2017-09-29 19:50 +0200
          Re: [PATCH -tip v3 7/7] kprobes: Use synchronize_rcu_tasks() for  optprobe with CONFIG_PREEMPT Masami Hiramatsu <mhiramat@kernel.org> - 2017-09-30 07:20 +0200

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