1 files changed, 47 insertions, 9 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 417a96bf3d41..142dbabc1615 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7645,16 +7645,9 @@ SYSCALL_DEFINE5(perf_event_open,
 
 		perf_remove_from_context(group_leader, false);
 
-		/*
-		 * Removing from the context ends up with disabled
-		 * event. What we want here is event in the initial
-		 * startup state, ready to be add into new context.
-		 */
-		perf_event__state_init(group_leader);
 		list_for_each_entry(sibling, &group_leader->sibling_list,
 				    group_entry) {
 			perf_remove_from_context(sibling, false);
-			perf_event__state_init(sibling);
 			put_ctx(gctx);
 		}
 	} else {
@@ -7670,13 +7663,31 @@ SYSCALL_DEFINE5(perf_event_open,
 		 */
 		synchronize_rcu();
 
-		perf_install_in_context(ctx, group_leader, group_leader->cpu);
-		get_ctx(ctx);
+		/*
+		 * Install the group siblings before the group leader.
+		 *
+		 * Because a group leader will try and install the entire group
+		 * (through the sibling list, which is still in-tact), we can
+		 * end up with siblings installed in the wrong context.
+		 *
+		 * By installing siblings first we NO-OP because they're not
+		 * reachable through the group lists.
+		 */
 		list_for_each_entry(sibling, &group_leader->sibling_list,
 				    group_entry) {
+			perf_event__state_init(sibling);
 			perf_install_in_context(ctx, sibling, sibling->cpu);
 			get_ctx(ctx);
 		}
+
+		/*
+		 * Removing from the context ends up with disabled
+		 * event. What we want here is event in the initial
+		 * startup state, ready to be add into new context.
+		 */
+		perf_event__state_init(group_leader);
+		perf_install_in_context(ctx, group_leader, group_leader->cpu);
+		get_ctx(ctx);
 	}
 
 	perf_install_in_context(ctx, event, event->cpu);
@@ -7806,8 +7817,35 @@ void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu)
 		list_add(&event->migrate_entry, &events);
 	}
 
+	/*
+	 * Wait for the events to quiesce before re-instating them.
+	 */
 	synchronize_rcu();
 
+	/*
+	 * Re-instate events in 2 passes.
+	 *
+	 * Skip over group leaders and only install siblings on this first
+	 * pass, siblings will not get enabled without a leader, however a
+	 * leader will enable its siblings, even if those are still on the old
+	 * context.
+	 */
+	list_for_each_entry_safe(event, tmp, &events, migrate_entry) {
+		if (event->group_leader == event)
+			continue;
+
+		list_del(&event->migrate_entry);
+		if (event->state >= PERF_EVENT_STATE_OFF)
+			event->state = PERF_EVENT_STATE_INACTIVE;
+		account_event_cpu(event, dst_cpu);
+		perf_install_in_context(dst_ctx, event, dst_cpu);
+		get_ctx(dst_ctx);
+	}
+
+	/*
+	 * Once all the siblings are setup properly, install the group leaders
+	 * to make it go.
+	 */
 	list_for_each_entry_safe(event, tmp, &events, migrate_entry) {
 		list_del(&event->migrate_entry);
 		if (event->state >= PERF_EVENT_STATE_OFF)