Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull perf fix from Thomas Gleixner:
 "A single fix for the intel cqm perf facility to prevent IPIs from
  interrupt context"

* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf/x86/intel/cqm: Return cached counter value from IRQ context

Author: torvalds

arch/x86/kernel/cpu/perf_event_intel_cqm.c

@@ -951,6 +951,14 @@ static u64 intel_cqm_event_count(struct perf_event *event)
 	if (!cqm_group_leader(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