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

1 files changed, 8 insertions, 0 deletions

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.