[Artful][PATCH 09/12] powerpc/perf: Fix usage of nest_imc_refc

[Gustavo Walbon]

From: Madhavan Srinivasan <maddy at linux.vnet.ibm.com>

BugLink: https://bugs.launchpad.net/bugs/1481347

nest_imc_refc is a reference count struct, used to track number of
active perf sessions using the nest units.

Currently the code accesses nest_imc_refc using node_id, which is
incorrect, the array is indexed by node number. Meaning in the case of
sparse node ids we index off the end of the array.

Fix it to use get_nest_pmu_ref() which uses the existing per-cpu
variable local_nest_imc_refc.

Fixes: 885dcd709ba91 ('powerpc/perf: Add nest IMC PMU support')
Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
Signed-off-by: Madhavan Srinivasan <maddy at linux.vnet.ibm.com>
[mpe: Tweak change log]
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
(cherry-picked from 711bd207a233141308d0aea0d2e286ee6b4b23cd)
Signed-off-by: Gustavo Walbon <gwalbon at linux.vnet.ibm.com>
---
 arch/powerpc/perf/imc-pmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index a8f95f96d54b..9ccac86f3463 100644
--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c
@@ -404,7 +404,7 @@ static void nest_imc_counters_release(struct perf_event *event)
 		rc = opal_imc_counters_stop(OPAL_IMC_COUNTERS_NEST,
 					    get_hard_smp_processor_id(event->cpu));
 		if (rc) {
-			mutex_unlock(&nest_imc_refc[node_id].lock);
+			mutex_unlock(&ref->lock);
 			pr_err("nest-imc: Unable to stop the counters for core %d\n", node_id);
 			return;
 		}
@@ -487,7 +487,7 @@ static int nest_imc_event_init(struct perf_event *event)
 		rc = opal_imc_counters_start(OPAL_IMC_COUNTERS_NEST,
 					     get_hard_smp_processor_id(event->cpu));
 		if (rc) {
-			mutex_unlock(&nest_imc_refc[node_id].lock);
+			mutex_unlock(&ref->lock);
 			pr_err("nest-imc: Unable to start the counters for node %d\n",
 									node_id);
 			return rc;
-- 
2.13.3