[PATCH v2] powerpc/perf: Fix core-imc hotplug callback failure during imc initialization

[Anju T Sudhakar]

From: Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx>

Call trace observed during boot:

[    0.750749] PCI: CLS 0 bytes, default 128
[    0.750855] Unpacking initramfs...
[    1.570445] Freeing initrd memory: 23168K
[    1.571090] rtas_flash: no firmware flash support
[    1.573873] nest_capp0_imc performance monitor hardware support registered
[    1.574006] nest_capp1_imc performance monitor hardware support registered
[    1.579616] core_imc memory allocation for cpu 56 failed
[    1.579730] Unable to handle kernel paging request for data at address 0xffa400010
[    1.579797] Faulting instruction address: 0xc000000000bf3294
0:mon> e
cpu 0x0: Vector: 300 (Data Access) at [c000000ff38ff8d0]
    pc: c000000000bf3294: mutex_lock+0x34/0x90
    lr: c000000000bf3288: mutex_lock+0x28/0x90
    sp: c000000ff38ffb50
   msr: 9000000002009033
   dar: ffa400010
 dsisr: 80000
  current = 0xc000000ff383de00
  paca    = 0xc000000007ae0000	 softe: 0	 irq_happened: 0x01
    pid   = 13, comm = cpuhp/0
Linux version 4.11.0-39.el7a.ppc64le (mockbuild@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx) (gcc version 4.8.5 20150623 (Red Hat 4.8.5-16) (GCC) ) #1 SMP Tue Oct 3 07:42:44 EDT 2017
0:mon> t
[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: Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Anju T Sudhakar <anju@xxxxxxxxxxxxxxxxxx>   
---
 arch/powerpc/perf/imc-pmu.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index 8812624..a7a1db4 100644
--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c
@@ -607,6 +607,20 @@ 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 an 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);
 
-- 
2.7.4