powerpc/perf: Fix kfree memory allocated for nest pmus

imc_common_cpuhp_mem_free() is the common function for all
IMC (In-memory Collection counters) domains to unregister cpuhotplug
callback and free memory. Since kfree of memory allocated for
nest-imc (per_nest_pmu_arr) is in the common code, all
domains (core/nest/thread) can do the kfree in the failure case.

This could potentially create a call trace as shown below, where
core(/thread/nest) imc pmu initialization fails and in the failure
path imc_common_cpuhp_mem_free() free the memory(per_nest_pmu_arr),
which is allocated by successfully registered nest units.

The call trace is generated in a scenario where core-imc
initialization is made to fail and a cpuhotplug is performed in a p9
system. During cpuhotplug ppc_nest_imc_cpu_offline() tries to access
per_nest_pmu_arr, which is already freed by core-imc.

NIP [c000000000cb6a94] mutex_lock+0x34/0x90
LR [c000000000cb6a88] mutex_lock+0x28/0x90
Call Trace:
mutex_lock+0x28/0x90 (unreliable)
perf_pmu_migrate_context+0x90/0x3a0
ppc_nest_imc_cpu_offline+0x190/0x1f0
cpuhp_invoke_callback+0x160/0x820
cpuhp_thread_fun+0x1bc/0x270
smpboot_thread_fn+0x250/0x290
kthread+0x1a8/0x1b0
ret_from_kernel_thread+0x5c/0x74

To address this scenario do the kfree(per_nest_pmu_arr) only in case
of nest-imc initialization failure, and when there is no other nest
units registered.

Fixes: 73ce9aec65b1 ("powerpc/perf: Fix IMC_MAX_PMU macro")
Signed-off-by: Anju T Sudhakar <[e-mail]>
Reviewed-by: Madhavan Srinivasan <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>

arch/powerpc/perf/imc-pmu.c

···
 		if (nest_pmus == 1) {
 			cpuhp_remove_state(CPUHP_AP_PERF_POWERPC_NEST_IMC_ONLINE);
 			kfree(nest_imc_refc);
+			kfree(per_nest_pmu_arr);
 		}
 
 		if (nest_pmus > 0)
···
 		kfree(pmu_ptr->attr_groups[IMC_EVENT_ATTR]->attrs);
 	kfree(pmu_ptr->attr_groups[IMC_EVENT_ATTR]);
 	kfree(pmu_ptr);
-	kfree(per_nest_pmu_arr);
 	return;
 }
 
···
 			ret = nest_pmu_cpumask_init();
 			if (ret) {
 				mutex_unlock(&nest_init_lock);
+				kfree(nest_imc_refc);
+				kfree(per_nest_pmu_arr);
 				goto err_free;
 			}
 		}