Messages in this thread | | | Date | Mon, 2 Mar 2009 19:00:27 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [RFC][PATCH] x86: make text_poke() atomic |
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* Ingo Molnar (mingo@elte.hu) 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. > > So indeed a new global lock is needed there. > > It's fixable and we'll fixit, but text_poke() is really more > complex than i'd like it to be. > > stop_machine_run() is essentially instantaneous in practice and > obviously serializing so it warrants a second look at least. > Have you tried to use it in kprobes? > > Ingo
This is why I prepared
text-edit-lock-architecture-independent-code.patch text-edit-lock-kprobes-architecture-independent-support.patch
A while ago. I'll post them right away.
Mathieu
-- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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