Patch "perf/x86/intel: Handle exclusive threadid correctly on CPU hotplug" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

perf/x86/intel: Handle exclusive threadid correctly on CPU hotplug

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
perf-x86-intel-handle-exclusive-threadid-correctly-on-cpu-hotplug.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Zhou Chengming <[email protected]>
Date: Mon, 16 Jan 2017 11:21:11 +0800
Subject: perf/x86/intel: Handle exclusive threadid correctly on CPU hotplug

From: Zhou Chengming <[email protected]>

[ Upstream commit 4e71de7986386d5fd3765458f27d612931f27f5e ]

The CPU hotplug function intel_pmu_cpu_starting() sets cpu_hw_events.excl_thread_id unconditionally to 1 when the shared exclusive counters data structure is already availabe for the sibling thread.

This works during the boot process because the first sibling gets threadid 0 assigned and the second sibling which shares the data structure gets 1.

But when the first thread of the core is offlined and onlined again it shares the data structure with the second thread and gets exclusive thread id 1 assigned as well.

Prevent this by checking the threadid of the already online thread.

[ tglx: Rewrote changelog ]

---
 arch/x86/events/intel/core.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

@@ -3164,13 +3164,16 @@ static void intel_pmu_cpu_starting(int c
 
 	if (x86_pmu.flags & PMU_FL_EXCL_CNTRS) {
 		for_each_cpu(i, topology_sibling_cpumask(cpu)) {
+			struct cpu_hw_events *sibling;
 			struct intel_excl_cntrs *c;
 
-			c = per_cpu(cpu_hw_events, i).excl_cntrs;
+			sibling = &per_cpu(cpu_hw_events, i);
+			c = sibling->excl_cntrs;
 			if (c && c->core_id == core_id) {
 				cpuc->kfree_on_online[1] = cpuc->excl_cntrs;
 				cpuc->excl_cntrs = c;
-				cpuc->excl_thread_id = 1;
+				if (!sibling->excl_thread_id)
+					cpuc->excl_thread_id = 1;
 				break;
 			}
 		}

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/perf-x86-intel-handle-exclusive-threadid-correctly-on-cpu-hotplug.patch