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    SubjectRe: [PATCH] oprofile: fix CPU unplug panic in ppro_stop()
    On 02.12.08 09:17:29, Ingo Molnar wrote:
    >
    > * Eric Dumazet <dada1@cosmosbay.com> wrote:
    >
    > > If oprofile statically compiled in kernel, a cpu unplug triggers
    > > a panic in ppro_stop(), because a NULL pointer is dereferenced.
    > >
    > > Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
    > > ---
    > > arch/x86/oprofile/op_model_ppro.c | 4 ++++
    > > 1 files changed, 4 insertions(+)
    >
    > > diff --git a/arch/x86/oprofile/op_model_ppro.c b/arch/x86/oprofile/op_model_ppro.c
    > > index 716d26f..e9f80c7 100644
    > > --- a/arch/x86/oprofile/op_model_ppro.c
    > > +++ b/arch/x86/oprofile/op_model_ppro.c
    > > @@ -156,6 +156,8 @@ static void ppro_start(struct op_msrs const * const msrs)
    > > unsigned int low, high;
    > > int i;
    > >
    > > + if (!reset_value)
    > > + return;
    > >
    > > for (i = 0; i < num_counters; ++i) {
    > > if (reset_value[i]) {
    > > CTRL_READ(low, high, msrs, i);

    The patch fixes the null pointer access and this ok. But the root
    cause seems to be in the cpu hotplug and initialization
    code. xxx_start() should not be called before xxx_setup_ctrs() or
    after xxx_shutdown(). Also, running only xxx_start() and xxx_stop() in
    the cpu notifier functions is not sufficient. There is at least some
    on_each_cpu code in nmi_setup() that should be called also in the cpu
    notifier functions. I have to review that code.

    [...]

    > It was absolutely unnecessary to add kmalloc to this rarely executed
    > codepath - and the way it was added was absolutely horrible as well, it
    > was tacked on in the middle of an existing codepath, instead of factoring
    > it out nicely. Perfmon will eventually replace PMC management anyway, so
    > there was no "this way it's cleaner" argument either. So this code should
    > have been changed minimally, instead of slapping in a full kmalloc for a
    > simple array extension from 2 to 4 entries ...

    Ingo, you are right that using kmalloc is unnecessary for
    reset_value. So, Andi, maybe you could make this code easier?

    -Robert

    --
    Advanced Micro Devices, Inc.
    Operating System Research Center
    email: robert.richter@amd.com



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