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Date: Wed, 4 Oct 2017 12:20:52 +0530
From: Anju T Sudhakar <anju@...ux.vnet.ibm.com>
To: mpe@...erman.id.au
Cc: linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
maddy@...ux.vnet.ibm.com, hemant@...ux.vnet.ibm.com,
anju@...ux.vnet.ibm.com
Subject: [PATCH] powerpc/perf: Fix for core/nest imc call trace on cpuhotplug
Nest/core pmu units are enabled only when it is used. A reference count is
maintained for the events which uses the nest/core pmu units. Currently in
*_imc_counters_release function a WARN() is used for notification of any
underflow of ref count.
The case where event ref count hit a negative value is, when perf session is
started, followed by offlining of all cpus in a given core.
i.e. in cpuhotplug offline path ppc_core_imc_cpu_offline() function set the
ref->count to zero, if the current cpu which is about to offline is the last
cpu in a given core and make an OPAL call to disable the engine in that core.
And on perf session termination, perf->destroy (core_imc_counters_release) will
first decrement the ref->count for this core and based on the ref->count value
an opal call is made to disable the core-imc engine.
Now, since cpuhotplug path already clears the ref->count for core and disabled
the engine, perf->destroy() decrementing again at event termination make it
negative which in turn fires the WARN_ON. The same happens for nest units.
Add a check to see if the reference count is alreday zero, before decrementing
the count, so that the ref count will not hit a negative value.
Signed-off-by: Anju T Sudhakar <anju@...ux.vnet.ibm.com>
---
arch/powerpc/perf/imc-pmu.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index 9ccac86f3463..e3a1f65933b5 100644
--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c
@@ -399,6 +399,20 @@ static void nest_imc_counters_release(struct perf_event *event)
/* Take the mutex lock for this node and then decrement the reference count */
mutex_lock(&ref->lock);
+ if (ref->refc == 0) {
+ /*
+ * The scenario where this is true is, when perf session is
+ * started, followed by offlining of all cpus in a given node.
+ *
+ * In the cpuhotplug offline path, ppc_nest_imc_cpu_offline()
+ * function set the ref->count to zero, if the cpu which is
+ * about to offline is the last cpu in a given node and make
+ * an OPAL call to disable the engine in that node.
+ *
+ */
+ mutex_unlock(&ref->lock);
+ return;
+ }
ref->refc--;
if (ref->refc == 0) {
rc = opal_imc_counters_stop(OPAL_IMC_COUNTERS_NEST,
@@ -646,6 +660,20 @@ static void core_imc_counters_release(struct perf_event *event)
return;
mutex_lock(&ref->lock);
+ if (ref->refc == 0) {
+ /*
+ * The scenario where this is true is, when perf session is
+ * started, followed by offlining of all cpus in a given core.
+ *
+ * In the cpuhotplug offline path, ppc_core_imc_cpu_offline()
+ * function set the ref->count to zero, if the cpu which is
+ * about to offline is the last cpu in a given core and make
+ * an OPAL call to disable the engine in that core.
+ *
+ */
+ mutex_unlock(&ref->lock);
+ return;
+ }
ref->refc--;
if (ref->refc == 0) {
rc = opal_imc_counters_stop(OPAL_IMC_COUNTERS_CORE,
--
2.14.1
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