[PATCH v1 2/2] x86, perf,cqm: handle CPU hotplug

[Kanaka Juvva <kanaka.d.juvva@linux.intel.com>]

Added lock in event reader function. The cqm_pick_event_reader() function
accesses cqm_cpumask and it is critical section between this and
cqm_stable().

This situation is true when a CPU is hotplugged. Mutex is used to protect
the critical section.

Signed-off-by: Kanaka Juvva <kanaka.d.juvva@linux.intel.com>
---
 arch/x86/kernel/cpu/perf_event_intel_cqm.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_cqm.c b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
index 1880761..e17e37f 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
@@ -1239,12 +1239,15 @@ static inline void cqm_pick_event_reader(int cpu)
 	int phys_id = topology_physical_package_id(cpu);
 	int i;
 
+	mutex_lock(&cache_mutex);
 	for_each_cpu(i, &cqm_cpumask) {
 		if (phys_id == topology_physical_package_id(i))
-			return;	/* already got reader for this socket */
+			goto out; /* already got reader for this socket */
 	}
 
 	cpumask_set_cpu(cpu, &cqm_cpumask);
+out:
+	mutex_unlock(&cache_mutex);
 }
 
 static void intel_cqm_cpu_prepare(unsigned int cpu)
-- 
2.1.0