Messages in this thread | | | Date | Mon, 02 Mar 2009 19:31:27 -0500 | From | Masami Hiramatsu <> | Subject | Re: [RFC][PATCH] x86: make text_poke() atomic |
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Ingo Molnar wrote: > * 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.
Yeah, kprobe_mutex protects text_poke from other kprobes, but not from other text_poke() users...
> 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.
Anyway, text_edit_lock ensures that.
By the way, I think set_fixmap/clear_fixmap seems simpler than kmap_atomic() variant. Would you think improving kmap_atomic_prot() is better?
> > Ingo > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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