[PATCH v3 29/46] perf/x86/intel/cmt: add error handling to intel_cmt_event_read

[David Carrillo-Cisneros]

First part of intel_cmt_event_read. Error conditions and placeholder
for oncoming chunks.

Signed-off-by: David Carrillo-Cisneros <davidcc@xxxxxxxxxx>
---
 arch/x86/events/intel/cmt.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/arch/x86/events/intel/cmt.c b/arch/x86/events/intel/cmt.c
index ef1000f..f5ab48e 100644
--- a/arch/x86/events/intel/cmt.c
+++ b/arch/x86/events/intel/cmt.c
@@ -1320,6 +1320,31 @@ static struct monr *monr_next_descendant_post(struct monr *pos,
 
 static int intel_cmt_event_read(struct perf_event *event)
 {
+	struct monr *monr = monr_from_event(event);
+
+	/*
+	 * preemption disabled since called holding
+	 * event's ctx->lock raw_spin_lock.
+	 */
+	WARN_ON_ONCE(!preempt_count());
+
+	/* terminated monrs are zombies and must not be read. */
+	if (WARN_ON_ONCE(monr->flags & CMT_MONR_ZOMBIE))
+		return -ENXIO;
+
+	/*
+	 * Only event parent can return a value, everyone else share its
+	 * rmid and therefore doesn't track occupancy independently.
+	 */
+	if (event->parent) {
+		local64_set(&event->count, 0);
+		return 0;
+	}
+
+	if (event->attach_state & PERF_ATTACH_TASK) {
+		/* To add support in next patches in series */
+		return -ENOTSUPP;
+	}
 	/* To add support in next patches in series */
 	return -ENOTSUPP;
 }
-- 
2.8.0.rc3.226.g39d4020