Re: [RFC PATCH 2/8] jump label v4 - x86: Introduce generic jumppatching without stop_machine
From: Mathieu Desnoyers
Date: Mon Jan 18 2010 - 13:33:18 EST
* Masami Hiramatsu (mhiramat@xxxxxxxxxx) wrote:
> Mathieu Desnoyers wrote:
> > * Arjan van de Ven (arjan@xxxxxxxxxxxxx) wrote:
> >> On Mon, 18 Jan 2010 10:59:30 -0500
> >> Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> >>> Yeah, so in the latest patch, I updated it to use int3 even if
> >>> len == 1. :-)
> >> int3 is not making a difference for your case; there is no guarantee
> >> that the other processor even sees the "int3 inbetween state" at all;
> >> if it's not safe without int3 then it won't be safe with int3 either.
> > What Masami means is that he updated his patch to use the int3+IPI
> > broadcast scheme.
> > Therefore, the CPUs not seeing the int3 inbetween state will be forced
> > to issue a serializing instruction while the int3 is in place anyway.
> By the way, in kprobes, we just use a text_poke() to put int3.
> I assume that we'd better send IPI afterward, wouldn't it?
Only if you need to ensure that you reached a state where all CPUs are
seeing the int3.
Note that kprobes already issues synchronize_sched() after breakpoint
removal, which should have a similar effect. However, AFAIK, it does not
synchronize after inserting the int3.
> Thank you,
> Masami Hiramatsu
> Software Engineer
> Hitachi Computer Products (America), Inc.
> Software Solutions Division
> e-mail: mhiramat@xxxxxxxxxx
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