[PATCHv3 bpf-next 5/8] ftrace: Add update_ftrace_direct_mod function

Jiri Olsa
2025-11-20T21:25:05Z

Adding update_ftrace_direct_mod function that modifies all entries
(ip -> direct) provided in hash argument to direct ftrace ops and
updates its attachments.

The difference to current modify_ftrace_direct is:
- hash argument that allows to modify multiple ip -> direct
entries at once

This change will allow us to have simple ftrace_ops for all bpf
direct interface users in following changes.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
include/linux/ftrace.h | 6 ++++
kernel/trace/ftrace.c | 68 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 74 insertions(+)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index c571deeff840..4e2c0ed769fc 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -552,6 +552,7 @@ int modify_ftrace_direct_nolock(struct ftrace_ops *ops, unsigned long addr);

int update_ftrace_direct_add(struct ftrace_ops *ops, struct ftrace_hash *hash);
int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash);
+int update_ftrace_direct_mod(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock);

void ftrace_stub_direct_tramp(void);

@@ -589,6 +590,11 @@ static inline int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace
return -ENODEV;
}

+static inline int update_ftrace_direct_mod(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock)
+{
+ return -ENODEV;
+}
+
/*
* This must be implemented by the architecture.
* It is the way the ftrace direct_ops helper, when called
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index cc730a8fd087..5243aefb6096 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6486,6 +6486,74 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash)
return err;
}

+int update_ftrace_direct_mod(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock)
+{
+ struct ftrace_hash *orig_hash = ops->func_hash->filter_hash;
+ struct ftrace_func_entry *entry, *tmp;
+ static struct ftrace_ops tmp_ops = {
+ .func = ftrace_stub,
+ .flags = FTRACE_OPS_FL_STUB,
+ };
+ unsigned long size, i;
+ int err;
+
+ 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);
+
+ /* 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);
+
+ 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 */

/**
--
2.51.1