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    Subject[PATCH AUTOSEL for 4.14 099/100] powerpc/perf/imc: Fix nest-imc cpuhotplug callback failure
    Date
    From: Anju T Sudhakar <anju@linux.vnet.ibm.com>

    [ Upstream commit ad2b6e01024ef23bddc3ce0bcb115ecd8c520b7e ]

    Oops is observed during boot:

    Faulting instruction address: 0xc000000000248340
    cpu 0x0: Vector: 380 (Data Access Out of Range) at [c000000ff66fb850]
    pc: c000000000248340: event_function_call+0x50/0x1f0
    lr: c00000000024878c: perf_remove_from_context+0x3c/0x100
    sp: c000000ff66fbad0
    msr: 9000000000009033
    dar: 7d20e2a6f92d03c0
    pid = 14, comm = cpuhp/0

    While registering the cpuhotplug callbacks for nest-imc, if we fail in
    the cpuhotplug online path for any random node in a multi node
    system (because the opal call to stop nest-imc counters fails for that
    node), ppc_nest_imc_cpu_offline() will get invoked for other nodes who
    successfully returned from cpuhotplug online path.

    This call trace is generated since in the ppc_nest_imc_cpu_offline()
    path we are trying to migrate the event context, when nest-imc
    counters are not even initialized.

    Patch to add a check to ensure that nest-imc is registered before
    migrating the event context.

    Fixes: 885dcd709ba9 ("powerpc/perf: Add nest IMC PMU support")
    Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
    Reviewed-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    arch/powerpc/perf/imc-pmu.c | 13 +++++++++++++
    1 file changed, 13 insertions(+)

    diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
    index cf64e16f92c2..da6ba9ba73ed 100644
    --- a/arch/powerpc/perf/imc-pmu.c
    +++ b/arch/powerpc/perf/imc-pmu.c
    @@ -309,6 +309,19 @@ static int ppc_nest_imc_cpu_offline(unsigned int cpu)
    return 0;

    /*
    + * Check whether nest_imc is registered. We could end up here if the
    + * cpuhotplug callback registration fails. i.e, callback invokes the
    + * offline path for all successfully registered nodes. At this stage,
    + * nest_imc pmu will not be registered and we should return here.
    + *
    + * We return with a zero since this is not an offline failure. And
    + * cpuhp_setup_state() returns the actual failure reason to the caller,
    + * which in turn will call the cleanup routine.
    + */
    + if (!nest_pmus)
    + return 0;
    +
    + /*
    * Now that this cpu is one of the designated,
    * find a next cpu a) which is online and b) in same chip.
    */
    --
    2.11.0
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