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

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Date:	Thu, 18 Jun 2015 11:49:29 -0700
From:	Kanaka Juvva <kanaka.d.juvva@...ux.intel.com>
To:	kanaka.d.juvva@...el.com, glenn.p.williamson@...el.com,
	matt.fleming@...el.com, will.auld@...el.com, andi@...stfloor.org,
	ananth.s.narayan@...el.com, linux-kernel@...r.kernel.org,
	andrew.j.herdrich@...el.com, tony.luck@...el.com,
	peterz@...radead.org, tglx@...utronix.de, x86@...nel.org,
	mingo@...hat.com, hpa@...or.com, luto@...capital.net,
	dvlasenk@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
	peter.p.waskiewicz.jr@...el.com, imammedo@...hat.com, bp@...e.de,
	ross.zwisler@...ux.intel.com, jacob.w.shin@...il.com,
	dirk.j.brandewie@...el.com, vikas.shivappa@...el.com,
	edwin.verplanke@...el.com, tomasz.kantecki@...el.com
Subject: [PATCH v1 2/2] x86, perf,cqm: handle CPU hotplug

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@...ux.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

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