Messages in this thread | | | Subject | Re: [PATCH 2/2] perf_counter: optimize context switch between identical inherited contexts | From | Peter Zijlstra <> | Date | Fri, 22 May 2009 11:02:00 +0200 |
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On Fri, 2009-05-22 at 10:57 +0200, Ingo Molnar wrote: > * Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > > On Fri, 2009-05-22 at 14:27 +1000, Paul Mackerras wrote: > > > > > The equivalence of contexts is detected by keeping a pointer in > > > each cloned context pointing to the context it was cloned from. > > > To cope with the situation where a context is changed by adding > > > or removing counters after it has been cloned, we also keep a > > > generation number on each context which is incremented every time > > > a context is changed. When a context is cloned we take a copy > > > of the parent's generation number, and two cloned contexts are > > > equivalent only if they have the same parent and the same > > > generation number. In order that the parent context pointer > > > remains valid (and is not reused), we increment the parent > > > context's reference count for each context cloned from it. > > > > > + u32 generation; > > > > Suppose someone writes a malicious proglet that inherits the > > counters, puts the child to sleep, does 2^32 mods on the counter > > set, and then wakes up the child. > > > > Would that merely corrupt the results, or make the kernel explode? > > i think it should be an u64.
So at to make the attack infeasible by death of the attacker and burnout of the solar-system? :-)
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