Re: [PATCH 1/2] perf_event: Fix incorrect range check on cpu number

[Corey Ashford]

Ingo Molnar wrote:
> * Corey Ashford <cjashfor@xxxxxxxxxxxxxxxxxx> 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

Oops! missed that.  Thanks!

- Corey


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