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Date:   Fri, 03 Nov 2017 11:19:58 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>,
        Anju T Sudhakar <anju@...ux.vnet.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/perf: Fix core-imc hotplug callback failure during imc initialization

Madhavan Srinivasan <maddy@...ux.vnet.ibm.com> writes:

> On Wednesday 01 November 2017 06:22 AM, Michael Ellerman wrote:
>> Anju T Sudhakar <anju@...ux.vnet.ibm.com> writes:
>>
>>> Call trace observed during boot:
>> What's the actual oops?
>
> I could recreate this in mambo with CPUS=2 and THREAD=2

That boots fine for me.

Presumably you've also done something to cause the CPU online to fail
and trigger the bug.

> Here is the complete stack trace.
>
> [    0.045367] core_imc memory allocation for cpu 2 failed
> [    0.045408] Unable to handle kernel paging request for data at 
> address 0x7d20e2a6f92d03b8
> [    0.045443] Faulting instruction address: 0xc0000000000dde18
> cpu 0x0: Vector: 380 (Data Access Out of Range) at [c0000000fd1cb890]
>      pc: c0000000000dde18: event_function_call+0x28/0x14c
>      lr: c0000000000dde00: event_function_call+0x10/0x14c
>      sp: c0000000fd1cbb10
>     msr: 9000000000009033
>     dar: 7d20e2a6f92d03b8
>    current = 0xc0000000fd15da00
>    paca    = 0xc00000000fff0000   softe: 0        irq_happened: 0x01
>      pid   = 11, comm = cpuhp/0
> Linux version 4.14.0-rc7-00014-g0a08377b127b (maddy@...hariSrinidhi) 
> (gcc version 5.4.0 20160609 (Ubuntu/IBM 5.4.0-6ubuntu1~16.04.1)) #5 SMP 
> Wed Nov 1 14:12:27 IST 2017
> enter ? for help
> [c0000000fd1cbb10] 0000000000000000 (unreliable)
> [c0000000fd1cbba0] c0000000000de180 perf_remove_from_context+0x30/0x9c
> [c0000000fd1cbbe0] c0000000000e9108 perf_pmu_migrate_context+0x9c/0x224
> [c0000000fd1cbc60] c0000000000682e0 ppc_core_imc_cpu_offline+0xdc/0x144
> [c0000000fd1cbcb0] c000000000070568 cpuhp_invoke_callback+0xe4/0x244
> [c0000000fd1cbd10] c000000000070824 cpuhp_thread_fun+0x15c/0x1b0
> [c0000000fd1cbd60] c00000000008e8cc smpboot_thread_fn+0x1e0/0x200
> [c0000000fd1cbdc0] c00000000008ae58 kthread+0x150/0x158
> [c0000000fd1cbe30] c00000000000b464 ret_from_kernel_thread+0x5c/0x78
>
>
>>
>>> [c000000ff38ffb80] c0000000002ddfac perf_pmu_migrate_context+0xac/0x470
>>> [c000000ff38ffc40] c00000000011385c ppc_core_imc_cpu_offline+0x1ac/0x1e0
>>> [c000000ff38ffc90] c000000000125758 cpuhp_invoke_callback+0x198/0x5d0
>>> [c000000ff38ffd00] c00000000012782c cpuhp_thread_fun+0x8c/0x3d0
>>> [c000000ff38ffd60] c0000000001678d0 smpboot_thread_fn+0x290/0x2a0
>>> [c000000ff38ffdc0] c00000000015ee78 kthread+0x168/0x1b0
>>> [c000000ff38ffe30] c00000000000b368 ret_from_kernel_thread+0x5c/0x74
>>>
>>> While registering the cpuhoplug callbacks for core-imc, if we fails
>>> in the cpuhotplug online path for any random core (either because opal call to
>>> initialize the core-imc counters fails or because memory allocation fails for
>>> that core), ppc_core_imc_cpu_offline() will get invoked for other cpus who
>>> successfully returned from cpuhotplug online path.
>>>
>>> But in the ppc_core_imc_cpu_offline() path we are trying to migrate the event
>>> context, when core-imc counters are not even initialized. Thus creating the
>>> above stack dump.
>>>
>>> Add a check to see if core-imc counters are enabled or not in the cpuhotplug
>>> offline path before migrating the context to handle this failing scenario.
>> Why do we need a bool to track this? Can't we just check the data
>> structure we're deinitialising has been initialised?
>
> My bad. yes we could do that. Something like this will work?
>
> @@ -606,6 +608,20 @@ static int ppc_core_imc_cpu_offline(unsigned int cpu)
>          if (!cpumask_test_and_clear_cpu(cpu, &core_imc_cpumask))
>                  return 0;
>
> +       /*
> +        * Check whether core_imc is registered. We could end up here
> +        * if the cpuhotplug callback registration fails. i.e, callback
> +        * invokes the offline path for all sucessfully registered cpus.
> +        * At this stage, core_imc pmu will not be registered and we
> +        * should return here.
> +        *
> +        * We return with a zero since this is not a offline failure.
> +        * And cpuhp_setup_state() returns the actual failure reason
> +        * to the caller, which inturn will call the cleanup routine.
> +        */
> +       if (!core_imc_pmu->pmu.event_init)
> +               return 0;
> +
>          /* Find any online cpu in that core except the current "cpu" */
>          ncpu = cpumask_any_but(cpu_sibling_mask(cpu), cpu);


That's not ideal, because you're grovelling into the details of the pmu
struct. But I guess it's OK for now.

cheers

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