@@ -28,6 +28,44 @@ extern tracepoint_ptr_t __stop___tracepo
DEFINE_SRCU(tracepoint_srcu);
EXPORT_SYMBOL_GPL(tracepoint_srcu);
+enum tp_transition_sync {
+ TP_TRANSITION_SYNC_1_0_1,
+ TP_TRANSITION_SYNC_N_2_1,
+
+ _NR_TP_TRANSITION_SYNC,
+};
+
+struct tp_transition_snapshot {
+ unsigned long rcu;
+ unsigned long srcu;
+ bool ongoing;
+};
+
+/* Protected by tracepoints_mutex */
+static struct tp_transition_snapshot tp_transition_snapshot[_NR_TP_TRANSITION_SYNC];
+
+static void tp_rcu_get_state(enum tp_transition_sync sync)
+{
+ struct tp_transition_snapshot *snapshot = &tp_transition_snapshot[sync];
+
+ /* Keep the latest get_state snapshot. */
+ snapshot->rcu = get_state_synchronize_rcu();
+ snapshot->srcu = start_poll_synchronize_srcu(&tracepoint_srcu);
+ snapshot->ongoing = true;
+}
+
+static void tp_rcu_cond_sync(enum tp_transition_sync sync)
+{
+ struct tp_transition_snapshot *snapshot = &tp_transition_snapshot[sync];
+
+ if (!snapshot->ongoing)
+ return;
+ cond_synchronize_rcu(snapshot->rcu);
+ if (!poll_state_synchronize_srcu(&tracepoint_srcu, snapshot->srcu))
+ synchronize_srcu(&tracepoint_srcu);
+ snapshot->ongoing = false;
+}
+
/* Set to 1 to enable tracepoint debug output */
static const int tracepoint_debug;
@@ -311,6 +349,11 @@ static int tracepoint_add_func(struct tr
*/
switch (nr_func_state(tp_funcs)) {
case TP_FUNC_1: /* 0->1 */
+ /*
+ * Make sure new static func never uses old data after a
+ * 1->0->1 transition sequence.
+ */
+ tp_rcu_cond_sync(TP_TRANSITION_SYNC_1_0_1);
/* Set static call to first function */
tracepoint_update_call(tp, tp_funcs);
/* Both iterator and static call handle NULL tp->funcs */
@@ -325,10 +368,15 @@ static int tracepoint_add_func(struct tr
* Requires ordering between RCU assign/dereference and
* static call update/call.
*/
- rcu_assign_pointer(tp->funcs, tp_funcs);
- break;
+ fallthrough;
case TP_FUNC_N: /* N->N+1 (N>1) */
rcu_assign_pointer(tp->funcs, tp_funcs);
+ /*
+ * Make sure static func never uses incorrect data after a
+ * N->...->2->1 (N>1) transition sequence.
+ */
+ if (tp_funcs[0].data != old[0].data)
+ tp_rcu_get_state(TP_TRANSITION_SYNC_N_2_1);
break;
default:
WARN_ON_ONCE(1);
@@ -372,24 +420,23 @@ static int tracepoint_remove_func(struct
/* Both iterator and static call handle NULL tp->funcs */
rcu_assign_pointer(tp->funcs, NULL);
/*
- * Make sure new func never uses old data after a 1->0->1
- * transition sequence.
- * Considering that transition 0->1 is the common case
- * and don't have rcu-sync, issue rcu-sync after
- * transition 1->0 to break that sequence by waiting for
- * readers to be quiescent.
+ * Make sure new static func never uses old data after a
+ * 1->0->1 transition sequence.
*/
- tracepoint_synchronize_unregister();
+ tp_rcu_get_state(TP_TRANSITION_SYNC_1_0_1);
break;
case TP_FUNC_1: /* 2->1 */
rcu_assign_pointer(tp->funcs, tp_funcs);
/*
- * On 2->1 transition, RCU sync is needed before setting
- * static call to first callback, because the observer
- * may have loaded any prior tp->funcs after the last one
- * associated with an rcu-sync.
+ * Make sure static func never uses incorrect data after a
+ * N->...->2->1 (N>2) transition sequence. If the first
+ * element's data has changed, then force the synchronization
+ * to prevent current readers that have loaded the old data
+ * from calling the new function.
*/
- tracepoint_synchronize_unregister();
+ if (tp_funcs[0].data != old[0].data)
+ tp_rcu_get_state(TP_TRANSITION_SYNC_N_2_1);
+ tp_rcu_cond_sync(TP_TRANSITION_SYNC_N_2_1);
/* Set static call to first function */
tracepoint_update_call(tp, tp_funcs);
break;
@@ -397,6 +444,12 @@ static int tracepoint_remove_func(struct
fallthrough;
case TP_FUNC_N:
rcu_assign_pointer(tp->funcs, tp_funcs);
+ /*
+ * Make sure static func never uses incorrect data after a
+ * N->...->2->1 (N>2) transition sequence.
+ */
+ if (tp_funcs[0].data != old[0].data)
+ tp_rcu_get_state(TP_TRANSITION_SYNC_N_2_1);
break;
default:
WARN_ON_ONCE(1);