1 files changed, 23 insertions, 1 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 866e85c5eb94..c8ba627c1d60 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -294,9 +294,31 @@ struct ring_buffer;
  */
 struct perf_event {
 #ifdef CONFIG_PERF_EVENTS
-        struct list_head                group_entry;
+        /*
+         * entry onto perf_event_context::event_list;
+         *   modifications require ctx->lock
+         *   RCU safe iterations.
+         */
         struct list_head                event_entry;
+
+        /*
+         * XXX: group_entry and sibling_list should be mutually exclusive;
+         * either you're a sibling on a group, or you're the group leader.
+         * Rework the code to always use the same list element.
+         *
+         * Locked for modification by both ctx->mutex and ctx->lock; holding
+         * either sufficies for read.
+         */
+        struct list_head                group_entry;
         struct list_head                sibling_list;
+
+        /*
+         * We need storage to track the entries in perf_pmu_migrate_context; we
+         * cannot use the event_entry because of RCU and we want to keep the
+         * group in tact which avoids us using the other two entries.
+         */
+        struct list_head                migrate_entry;
+
         struct hlist_node               hlist_entry;
         int                             nr_siblings;
         int                             group_flags;