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

    > Reported-by: Michael Neuling <mikey@neuling.org>
    > Tested-by: Michael Neuling <mikey@neuling.org>
    > Cc: stable@kernel.org
    > Signed-off-by: Paul Mackerras <paulus@samba.org>
    > ---
    > kernel/perf_event.c | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/kernel/perf_event.c b/kernel/perf_event.c
    > index 6b7ddba..78551b3 100644
    > --- a/kernel/perf_event.c
    > +++ b/kernel/perf_event.c
    > @@ -1604,7 +1604,7 @@ static struct perf_event_context *find_get_context(pid_t pid, int cpu)
    > if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
    > return ERR_PTR(-EACCES);
    >
    > - if (cpu < 0 || cpu > num_possible_cpus())
    > + if (cpu < 0 || cpu >= nr_cpumask_bits)
    > return ERR_PTR(-EINVAL);
    >
    > /*



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