[PATCHv5 bpf-next 5/9] ftrace: Add update_ftrace_direct_del function

Jiri Olsa
2025-12-15T21:15:08Z

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

The difference to current unregister_ftrace_direct is
- hash argument that allows to unregister multiple ip -> direct
entries at once
- we can call update_ftrace_direct_del multiple times on the
same ftrace_ops object, becase we do not need to unregister
all entries at once, we can do it gradualy with the help of
ftrace_update_ops function

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 | 112 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 118 insertions(+)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 5cf151cb8e6d..ac4b473c7fd3 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -544,6 +544,7 @@ int modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr);
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);

void ftrace_stub_direct_tramp(void);

@@ -576,6 +577,11 @@ static inline int update_ftrace_direct_add(struct ftrace_ops *ops, struct ftrace
return -ENODEV;
}

+static inline int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash)
+{
+ 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 ec7d93460dac..48dc0de5f2ce 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6377,6 +6377,118 @@ int update_ftrace_direct_add(struct ftrace_ops *ops, struct ftrace_hash *hash)
return err;
}

+/**
+ * hash_sub - substracts @b from @a and returns the result
+ * @a: struct ftrace_hash object
+ * @b: struct ftrace_hash object
+ *
+ * Returns struct ftrace_hash object on success, NULL on error.
+ */
+static struct ftrace_hash *hash_sub(struct ftrace_hash *a, struct ftrace_hash *b)
+{
+ struct ftrace_func_entry *entry, *del;
+ struct ftrace_hash *sub;
+ int size, i;
+
+ sub = alloc_and_copy_ftrace_hash(a->size_bits, a);
+ if (!sub)
+ goto error;
+
+ size = 1 << b->size_bits;
+ for (i = 0; i < size; i++) {
+ hlist_for_each_entry(entry, &b->buckets[i], hlist) {
+ del = __ftrace_lookup_ip(sub, entry->ip);
+ if (WARN_ON_ONCE(!del))
+ goto error;
+ remove_hash_entry(sub, del);
+ kfree(del);
+ }
+ }
+ return sub;
+
+ error:
+ free_ftrace_hash(sub);
+ return NULL;
+}
+
+int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash)
+{
+ struct ftrace_hash *old_direct_functions = NULL, *new_direct_functions;
+ struct ftrace_hash *old_filter_hash, *new_filter_hash = NULL;
+ struct ftrace_func_entry *del, *entry;
+ 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;
+
+ mutex_lock(&direct_mutex);
+
+ old_filter_hash = ops->func_hash ? ops->func_hash->filter_hash : NULL;
+
+ if (!hash_count(old_filter_hash))
+ goto out_unlock;
+
+ /* Make sure requested entries are already registered. */
+ size = 1 << hash->size_bits;
+ for (i = 0; i < size; i++) {
+ hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
+ del = __ftrace_lookup_ip(direct_functions, entry->ip);
+ if (!del || del->direct != entry->direct)
+ goto out_unlock;
+ }
+ }
+
+ err = -ENOMEM;
+ new_filter_hash = hash_sub(old_filter_hash, hash);
+ if (!new_filter_hash)
+ goto out_unlock;
+
+ new_direct_functions = hash_sub(direct_functions, hash);
+ if (!new_direct_functions)
+ goto out_unlock;
+
+ /* If there's nothing left, we need to unregister the ops. */
+ if (ftrace_hash_empty(new_filter_hash)) {
+ err = unregister_ftrace_function(ops);
+ if (!err) {
+ /* cleanup for possible another register call */
+ ops->func = NULL;
+ ops->trampoline = 0;
+ ftrace_free_filter(ops);
+ ops->func_hash->filter_hash = NULL;
+ }
+ } else {
+ err = ftrace_update_ops(ops, new_filter_hash, EMPTY_HASH);
+ /*
+ * new_filter_hash is dup-ed, so we need to release it anyway,
+ * old_filter_hash either stays on error or is already released
+ */
+ }
+
+ if (err) {
+ /* free the new_direct_functions */
+ old_direct_functions = new_direct_functions;
+ } else {
+ rcu_assign_pointer(direct_functions, new_direct_functions);
+ }
+
+ out_unlock:
+ mutex_unlock(&direct_mutex);
+
+ if (old_direct_functions && old_direct_functions != EMPTY_HASH)
+ call_rcu_tasks(&old_direct_functions->rcu, register_ftrace_direct_cb);
+ free_ftrace_hash(new_filter_hash);
+
+ return err;
+}
+
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */

/**
--
2.52.0