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-rw-r--r--kernel/tracepoint.c102
1 files changed, 82 insertions, 20 deletions
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 133b6454b287..8d772bd6894d 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -15,6 +15,13 @@
#include <linux/sched/task.h>
#include <linux/static_key.h>
+enum tp_func_state {
+ TP_FUNC_0,
+ TP_FUNC_1,
+ TP_FUNC_2,
+ TP_FUNC_N,
+};
+
extern tracepoint_ptr_t __start___tracepoints_ptrs[];
extern tracepoint_ptr_t __stop___tracepoints_ptrs[];
@@ -246,26 +253,29 @@ static void *func_remove(struct tracepoint_func **funcs,
return old;
}
-static void tracepoint_update_call(struct tracepoint *tp, struct tracepoint_func *tp_funcs, bool sync)
+/*
+ * Count the number of functions (enum tp_func_state) in a tp_funcs array.
+ */
+static enum tp_func_state nr_func_state(const struct tracepoint_func *tp_funcs)
+{
+ if (!tp_funcs)
+ return TP_FUNC_0;
+ if (!tp_funcs[1].func)
+ return TP_FUNC_1;
+ if (!tp_funcs[2].func)
+ return TP_FUNC_2;
+ return TP_FUNC_N; /* 3 or more */
+}
+
+static void tracepoint_update_call(struct tracepoint *tp, struct tracepoint_func *tp_funcs)
{
void *func = tp->iterator;
/* Synthetic events do not have static call sites */
if (!tp->static_call_key)
return;
-
- if (!tp_funcs[1].func) {
+ if (nr_func_state(tp_funcs) == TP_FUNC_1)
func = tp_funcs[0].func;
- /*
- * If going from the iterator back to a single caller,
- * we need to synchronize with __DO_TRACE to make sure
- * that the data passed to the callback is the one that
- * belongs to that callback.
- */
- if (sync)
- tracepoint_synchronize_unregister();
- }
-
__static_call_update(tp->static_call_key, tp->static_call_tramp, func);
}
@@ -299,9 +309,31 @@ static int tracepoint_add_func(struct tracepoint *tp,
* a pointer to it. This array is referenced by __DO_TRACE from
* include/linux/tracepoint.h using rcu_dereference_sched().
*/
- tracepoint_update_call(tp, tp_funcs, false);
- rcu_assign_pointer(tp->funcs, tp_funcs);
- static_key_enable(&tp->key);
+ switch (nr_func_state(tp_funcs)) {
+ case TP_FUNC_1: /* 0->1 */
+ /* Set static call to first function */
+ tracepoint_update_call(tp, tp_funcs);
+ /* Both iterator and static call handle NULL tp->funcs */
+ rcu_assign_pointer(tp->funcs, tp_funcs);
+ static_key_enable(&tp->key);
+ break;
+ case TP_FUNC_2: /* 1->2 */
+ /* Set iterator static call */
+ tracepoint_update_call(tp, tp_funcs);
+ /*
+ * Iterator callback installed before updating tp->funcs.
+ * Requires ordering between RCU assign/dereference and
+ * static call update/call.
+ */
+ rcu_assign_pointer(tp->funcs, tp_funcs);
+ break;
+ case TP_FUNC_N: /* N->N+1 (N>1) */
+ rcu_assign_pointer(tp->funcs, tp_funcs);
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ break;
+ }
release_probes(old);
return 0;
@@ -328,17 +360,47 @@ static int tracepoint_remove_func(struct tracepoint *tp,
/* Failed allocating new tp_funcs, replaced func with stub */
return 0;
- if (!tp_funcs) {
+ switch (nr_func_state(tp_funcs)) {
+ case TP_FUNC_0: /* 1->0 */
/* Removed last function */
if (tp->unregfunc && static_key_enabled(&tp->key))
tp->unregfunc();
static_key_disable(&tp->key);
+ /* Set iterator static call */
+ tracepoint_update_call(tp, tp_funcs);
+ /* 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.
+ */
+ tracepoint_synchronize_unregister();
+ break;
+ case TP_FUNC_1: /* 2->1 */
rcu_assign_pointer(tp->funcs, tp_funcs);
- } else {
+ /*
+ * 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.
+ */
+ tracepoint_synchronize_unregister();
+ /* Set static call to first function */
+ tracepoint_update_call(tp, tp_funcs);
+ break;
+ case TP_FUNC_2: /* N->N-1 (N>2) */
+ fallthrough;
+ case TP_FUNC_N:
rcu_assign_pointer(tp->funcs, tp_funcs);
- tracepoint_update_call(tp, tp_funcs,
- tp_funcs[0].data != old[0].data);
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ break;
}
release_probes(old);
return 0;