On Sat, Aug 16, 2025 at 10:50 PM Masami Hiramatsu [off-list ref] wrote:

Hi Menglong,

Sorry, one more thing.

quoted

@@ -260,14 +263,12 @@ static int fprobe_entry(struct ftrace_graph_ent *trace, struct fgraph_ops *gops,
      if (WARN_ON_ONCE(!fregs))
              return 0;

-     first = node = find_first_fprobe_node(func);
-     if (unlikely(!first))
-             return 0;
-
+     rcu_read_lock();

Actually, we don't need these rcu_read_lock() in this function, because
the caller function_graph_enter_regs() uses ftrace_test_recursion_trylock()
which disables preemption. Thus we don't need to do this again here.

Yeah, I understand it now. I wondered about this part
for a long time, as I didn't see any RCU lock in the
fprobe_entry(). Thanks for the explanation ;)

I'll send a V5 now.

quoted

+     head = rhltable_lookup(&fprobe_ip_table, &func, fprobe_rht_params);
      reserved_words = 0;
-     hlist_for_each_entry_from_rcu(node, hlist) {
+     rhl_for_each_entry_rcu(node, pos, head, hlist) {
              if (node->addr != func)
-                     break;
+                     continue;
              fp = READ_ONCE(node->fp);
              if (!fp || !fp->exit_handler)
                      continue;

@@ -278,17 +279,19 @@ static int fprobe_entry(struct ftrace_graph_ent *trace, struct fgraph_ops *gops,
              reserved_words +=
                      FPROBE_HEADER_SIZE_IN_LONG + SIZE_IN_LONG(fp->entry_data_size);
      }
-     node = first;
+     rcu_read_unlock();
      if (reserved_words) {
              fgraph_data = fgraph_reserve_data(gops->idx, reserved_words * sizeof(long));
              if (unlikely(!fgraph_data)) {
-                     hlist_for_each_entry_from_rcu(node, hlist) {
+                     rcu_read_lock();

Ditto.

quoted

+                     rhl_for_each_entry_rcu(node, pos, head, hlist) {
                              if (node->addr != func)
-                                     break;
+                                     continue;
                              fp = READ_ONCE(node->fp);
                              if (fp && !fprobe_disabled(fp))
                                      fp->nmissed++;
                      }
+                     rcu_read_unlock();
                      return 0;
              }
      }

Thank you,


--
Masami Hiramatsu (Google) [off-list ref]