Re: [PATCHv5 bpf-next 6/9] ftrace: Add update_ftrace_direct_mod function
From: Steven Rostedt <rostedt@goodmis.org>
Date: 2025-12-18 15:18:10
Also in:
bpf, linux-arm-kernel, lkml
On Mon, 15 Dec 2025 22:13:59 +0100 Jiri Olsa [off-list ref] wrote:
quoted hunk ↗ jump to hunk
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 48dc0de5f2ce..95a38fb18ed7 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c@@ -6489,6 +6489,78 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash) return err; }
Kerneldoc needed.
+int update_ftrace_direct_mod(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock)
+{
+ struct ftrace_func_entry *entry, *tmp;
+ static struct ftrace_ops tmp_ops = {
+ .func = ftrace_stub,
+ .flags = FTRACE_OPS_FL_STUB,
+ };
+ struct ftrace_hash *orig_hash;
+ unsigned long size, i;
+ int err = -EINVAL;
+
+ if (!hash_count(hash))
+ return -EINVAL;
+ if (check_direct_multi(ops))
+ return -EINVAL;
+ if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
+ return -EINVAL;
+ if (direct_functions == EMPTY_HASH)
+ return -EINVAL;
+
+ if (do_direct_lock)
+ mutex_lock(&direct_mutex);This optional taking of the direct_mutex lock needs some serious rationale and documentation.
+ + orig_hash = ops->func_hash ? ops->func_hash->filter_hash : NULL; + if (!orig_hash) + goto unlock; + + /* Enable the tmp_ops to have the same functions as the direct ops */ + ftrace_ops_init(&tmp_ops); + tmp_ops.func_hash = ops->func_hash; + + err = register_ftrace_function_nolock(&tmp_ops); + if (err) + goto unlock; + + /* + * Call __ftrace_hash_update_ipmodify() here, so that we can call + * ops->ops_func for the ops. This is needed because the above + * register_ftrace_function_nolock() worked on tmp_ops. + */ + err = __ftrace_hash_update_ipmodify(ops, orig_hash, orig_hash, true); + if (err) + goto out; + + /* + * Now the ftrace_ops_list_func() is called to do the direct callers. + * We can safely change the direct functions attached to each entry. + */ + mutex_lock(&ftrace_lock);
I'm going to need some time staring at this code. It looks like it may be relying on some internals here. -- Steve
+
+ size = 1 << hash->size_bits;
+ for (i = 0; i < size; i++) {
+ hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
+ tmp = __ftrace_lookup_ip(direct_functions, entry->ip);
+ if (!tmp)
+ continue;
+ tmp->direct = entry->direct;
+ }
+ }
+
+ mutex_unlock(&ftrace_lock);
+
+out:
+ /* Removing the tmp_ops will add the updated direct callers to the functions */
+ unregister_ftrace_function(&tmp_ops);
+
+unlock:
+ if (do_direct_lock)
+ mutex_unlock(&direct_mutex);
+ return err;
+}
+
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
/**