On Thu, Aug 14, 2025 at 11:40 PM Masami Hiramatsu [off-list ref] wrote:

On Thu, 31 Jul 2025 17:24:24 +0800
Menglong Dong [off-list ref] wrote:

quoted

For now, all the kernel functions who are hooked by the fprobe will be
added to the hash table "fprobe_ip_table". The key of it is the function
address, and the value of it is "struct fprobe_hlist_node".

The budget of the hash table is FPROBE_IP_TABLE_SIZE, which is 256. And
this means the overhead of the hash table lookup will grow linearly if
the count of the functions in the fprobe more than 256. When we try to
hook all the kernel functions, the overhead will be huge.

Therefore, replace the hash table with rhltable to reduce the overhead.

Hi Menglong,

Thanks for update, I have just some nitpicks.

quoted

Signed-off-by: Menglong Dong <redacted>
---
v3:
- some format optimization
- handle the error that returned from rhltable_insert in
  insert_fprobe_node
---
 include/linux/fprobe.h |   3 +-
 kernel/trace/fprobe.c  | 154 +++++++++++++++++++++++------------------
 2 files changed, 90 insertions(+), 67 deletions(-)

diff --git a/include/linux/fprobe.h b/include/linux/fprobe.h
index 702099f08929..f5d8982392b9 100644
--- a/include/linux/fprobe.h
+++ b/include/linux/fprobe.h

@@ -7,6 +7,7 @@
 #include <linux/ftrace.h>
 #include <linux/rcupdate.h>
 #include <linux/refcount.h>
+#include <linux/rhashtable.h>

nit: can you also include this header file in fprobe.c ?

OK!

quoted

 #include <linux/slab.h>

[......]

quoted

      mutex_lock(&fprobe_mutex);
-     for (i = 0; i < FPROBE_IP_TABLE_SIZE; i++)
-             fprobe_remove_node_in_module(mod, &fprobe_ip_table[i], &alist);
+     rhashtable_walk_enter(&fprobe_ip_table.ht, &iter);

nit: Use rhltable_walk_enter() instead.

OK!

I'll send the V4 later with these nitpicks fixed.

Thanks!
Menglong Dong

Others looks good to me.

Thank you,

quoted

+     do {
+             rhashtable_walk_start(&iter);
+
+             while ((node = rhashtable_walk_next(&iter)) && !IS_ERR(node))
+                     fprobe_remove_node_in_module(mod, node, &alist);
+
+             rhashtable_walk_stop(&iter);
+     } while (node == ERR_PTR(-EAGAIN));
+     rhashtable_walk_exit(&iter);

      if (alist.index < alist.size && alist.index > 0)
              ftrace_set_filter_ips(&fprobe_graph_ops.ops,

@@ -722,8 +729,16 @@ int register_fprobe_ips(struct fprobe *fp, unsigned long *addrs, int num)
      ret = fprobe_graph_add_ips(addrs, num);
      if (!ret) {
              add_fprobe_hash(fp);
-             for (i = 0; i < hlist_array->size; i++)
-                     insert_fprobe_node(&hlist_array->array[i]);
+             for (i = 0; i < hlist_array->size; i++) {
+                     ret = insert_fprobe_node(&hlist_array->array[i]);
+                     if (ret)
+                             break;
+             }
+             /* fallback on insert error */
+             if (ret) {
+                     for (i--; i >= 0; i--)
+                             delete_fprobe_node(&hlist_array->array[i]);
+             }
      }
      mutex_unlock(&fprobe_mutex);

@@ -819,3 +834,10 @@ int unregister_fprobe(struct fprobe *fp)
      return ret;
 }
 EXPORT_SYMBOL_GPL(unregister_fprobe);
+
+static int __init fprobe_initcall(void)
+{
+     rhltable_init(&fprobe_ip_table, &fprobe_rht_params);
+     return 0;
+}
+late_initcall(fprobe_initcall);
--

2.50.1

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