Messages in this thread | | | Date | Tue, 3 Mar 2009 01:22:14 +0100 | From | Ingo Molnar <> | Subject | Re: [RFC][PATCH] x86: make text_poke() atomic |
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* Masami Hiramatsu <mhiramat@redhat.com> wrote:
> > > Ingo Molnar wrote: > > * Masami Hiramatsu <mhiramat@redhat.com> wrote: > > > >> Ingo Molnar wrote: > >>>>> So perhaps another approach to (re-)consider would be to go back > >>>>> to atomic fixmaps here. It spends 3 slots but that's no big > >>>>> deal. > >>>> Oh, it's a good idea! fixmaps must make it simpler. > >>>> > >>>>> In exchange it will be conceptually simpler, and will also scale > >>>>> much better than a global spinlock. What do you think? > >>>> I think even if I use fixmaps, we have to use a spinlock to protect > >>>> the fixmap area from other threads... > >>> that's why i suggested to use an atomic-kmap, not a fixmap. > >> Even if the mapping is atomic, text_poke() has to protect pte > >> from other text_poke()s while changing code. > >> AFAIK, atomic-kmap itself doesn't ensure that, does it? > > > > Well, but text_poke() is not a serializing API to begin with. > > It's normally used in code patching sequences when we 'know' > > that there cannot be similar parallel activities. The kprobes > > usage of text_poke() looks unsafe - and that needs to be fixed. > > Oh, kprobes already prohibited parallel arming/disarming > by using kprobe_mutex. :-)
yeah, but still the API is somewhat unsafe.
In any case, you also answered your own question:
> >> Even if the mapping is atomic, text_poke() has to protect pte > >> from other text_poke()s while changing code. > >> AFAIK, atomic-kmap itself doesn't ensure that, does it?
kprobe_mutex does that.
Ingo
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