[GIT pull] perf fixes for 4.1

[GIT pull] perf fixes for 4.1

[Thomas Gleixner]

Linus,

please pull the latest perf-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git perf-urgent-for-linus

A single fix for the intel cqm perf facility to prevent IPIs from
interrupt context.

Thanks,

	tglx

------------------>
Matt Fleming (1):
      perf/x86/intel/cqm: Return cached counter value from IRQ context


 arch/x86/kernel/cpu/perf_event_intel_cqm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_cqm.c b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
index 188076161c1b..63eb68b73589 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
@@ -952,6 +952,14 @@ static u64 intel_cqm_event_count(struct perf_event *event)
 		return 0;
 
 	/*
+	 * Getting up-to-date values requires an SMP IPI which is not
+	 * possible if we're being called in interrupt context. Return
+	 * the cached values instead.
+	 */
+	if (unlikely(in_interrupt()))
+		goto out;
+
+	/*
 	 * Notice that we don't perform the reading of an RMID
 	 * atomically, because we can't hold a spin lock across the
 	 * IPIs.