Messages in this thread |  | | | Date | Tue, 15 Dec 2009 20:08:58 +0100 | | From | Ingo Molnar <> | | Subject | Re: [PATCH 1/2] perf_event: Fix incorrect range check on cpu number |
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* Corey Ashford <cjashfor@linux.vnet.ibm.com> wrote:
> > Paul Mackerras wrote: > >On Tue, Dec 15, 2009 at 11:31:32AM +0100, Peter Zijlstra wrote: > > > >>On Tue, 2009-12-15 at 19:40 +1100, Paul Mackerras wrote: > >>>It is quite legitimate for CPUs to be numbered sparsely, meaning that > >>>it possible for an online CPU to have a number which is greater than > >>>the total count of possible CPUs. > >>> > >>>Currently find_get_context() has a sanity check on the cpu number > >>>where it checks it against num_possible_cpus(). This test can fail > >>>for a legitimate cpu number if the cpu_possible_mask is sparsely > >>>populated. > >>> > >>>This fixes the problem by checking the CPU number against > >>>nr_cpumask_bits instead, since that is the appropriate check to ensure > >>>that the cpu number is same to pass to cpu_isset() subsequently. > >>Cute, do you actually have hardware that does this? > > > >Yeah, Mikey ran across this on a POWER7 box here. > > Does the perf tool need to be fixed too? The "perf stat" tool, at > least, has a "-a" switch that tells the tool to count the event on > all cpus, and it does this by iterating over the number of cpus, > 0..n, assuming they are all contiguous.
Yes, see patch 2/2 of this series.
Ingo
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