[PATCH] powerpc/perf: Fix core-imc hotplug callback failure during imc initialization

[Anju T Sudhakar <anju@linux.vnet.ibm.com>]

Call trace observed during boot:

[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.

Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
---
 arch/powerpc/perf/imc-pmu.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index 8812624..08139f9 100644
--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c
@@ -30,6 +30,7 @@ static struct imc_pmu *per_nest_pmu_arr[IMC_MAX_PMUS];
 static cpumask_t nest_imc_cpumask;
 struct imc_pmu_ref *nest_imc_refc;
 static int nest_pmus;
+static bool core_imc_enabled;
 
 /* Core IMC data structures and variables */
 
@@ -607,6 +608,19 @@ static int ppc_core_imc_cpu_offline(unsigned int cpu)
 	if (!cpumask_test_and_clear_cpu(cpu, &core_imc_cpumask))
 		return 0;
 
+	/*
+	 * See if core imc counters are enabled or not.
+	 *
+	 * Suppose we reach here from core_imc_cpumask_init(),
+	 * since we failed at the cpuhotplug online path for any random
+	 * core (either because opal call to initialize the core-imc counters
+	 * failed  or because memory allocation failed).
+	 * We need to check whether core imc counters are enabled or not before
+	 * migrating the event context from cpus in the other cores.
+	 */
+	if (!core_imc_enabled)
+		return 0;
+
 	/* Find any online cpu in that core except the current "cpu" */
 	ncpu = cpumask_any_but(cpu_sibling_mask(cpu), cpu);
 
@@ -1299,6 +1313,7 @@ int init_imc_pmu(struct device_node *parent, struct imc_pmu *pmu_ptr, int pmu_id
 			return ret;
 		}
 
+		core_imc_enabled = true;
 		break;
 	case IMC_DOMAIN_THREAD:
 		ret = thread_imc_cpu_init();
-- 
2.7.4