ftrace: Add update_ftrace_direct_del function

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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/bpf/20251230145010.103439-6-jolsa@kernel.org

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

kernel/trace/ftrace.c

@@ -6418,6 +6418,133 @@ 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;
+
+	sub = alloc_and_copy_ftrace_hash(a->size_bits, a);
+	if (!sub)
+		return NULL;
+
+	size = 1 << b->size_bits;
+	for (int 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)) {
+				free_ftrace_hash(sub);
+				return NULL;
+			}
+			remove_hash_entry(sub, del);
+			kfree(del);
+		}
+	}
+	return sub;
+}
+
+/**
+ * update_ftrace_direct_del - Updates @ops by removing its direct
+ * callers provided in @hash
+ * @ops: The address of the struct ftrace_ops object
+ * @hash: The address of the struct ftrace_hash object
+ *
+ * This is used to delete custom direct callers (ip -> addr) in
+ * @ops specified via @hash. The @ops will be either unregistered
+ * updated.
+ *
+ * Returns: zero on success. Non zero on error, which includes:
+ *  -EINVAL - The @hash is empty
+ *  -EINVAL - The @ops is not registered
+ */
+int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash)
+{
+	struct ftrace_hash *old_direct_functions = NULL;
+	struct ftrace_hash *new_direct_functions;
+	struct ftrace_hash *new_filter_hash = NULL;
+	struct ftrace_hash *old_filter_hash;
+	struct ftrace_func_entry *entry;
+	struct ftrace_func_entry *del;
+	unsigned long size;
+	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 (int 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 */
 
 /**