[RFC 03/10] ftrace: Add unregister_ftrace_direct_hash function

[Jiri Olsa <jolsa@xxxxxxxxxx>]

Adding unregister_ftrace_direct_hash function that unregisters
all entries (ip -> direct) provided in hash argument.

The difference to current unregister_ftrace_direct is
 - hash argument that allows to unregister multiple ip -> direct
   entries at once
 - we can call unregister_ftrace_direct_hash 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@xxxxxxxxxx>
---
 include/linux/ftrace.h |  6 +++
 kernel/trace/ftrace.c  | 98 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 104 insertions(+)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index e45bcc9de53b..7ff6004498c0 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -527,6 +527,7 @@ int modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr);
 int modify_ftrace_direct_nolock(struct ftrace_ops *ops, unsigned long addr);
 
 int register_ftrace_direct_hash(struct ftrace_ops *ops, struct ftrace_hash *hash);
+int unregister_ftrace_direct_hash(struct ftrace_ops *ops, struct ftrace_hash *hash);
 
 void ftrace_stub_direct_tramp(void);
 
@@ -559,6 +560,11 @@ int register_ftrace_direct_hash(struct ftrace_ops *ops, struct ftrace_hash *hash
 	return -ENODEV;
 }
 
+int unregister_ftrace_direct_hash(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 1dbb113f4e9c..d761237ec70f 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6342,6 +6342,104 @@ int register_ftrace_direct_hash(struct ftrace_ops *ops, struct ftrace_hash *hash
 }
 EXPORT_SYMBOL_GPL(register_ftrace_direct_hash);
 
+/**
+ * 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 unregister_ftrace_direct_hash(struct ftrace_ops *ops, struct ftrace_hash *hash)
+{
+	struct ftrace_hash *new_hash = NULL, *filter_hash = NULL, *free_hash = NULL;
+	struct ftrace_func_entry *del, *entry;
+	unsigned long size, i;
+	int err = -EINVAL;
+
+	if (!hash_count(hash))
+		return 0;
+	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);
+
+	/* 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;
+		}
+	}
+
+	filter_hash = hash_sub(ops->func_hash->filter_hash, hash);
+	if (!filter_hash)
+		goto out_unlock;
+
+	new_hash = hash_sub(direct_functions, hash);
+	if (!new_hash)
+		goto out_unlock;
+
+	/* If there's nothing left, we need to unregister the ops. */
+	if (ftrace_hash_empty(filter_hash)) {
+		err = unregister_ftrace_function(ops);
+		/* 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, filter_hash, EMPTY_HASH);
+	}
+
+	free_hash = direct_functions;
+	rcu_assign_pointer(direct_functions, new_hash);
+
+ out_unlock:
+	mutex_unlock(&direct_mutex);
+
+	if (free_hash && free_hash != EMPTY_HASH)
+		call_rcu_tasks(&free_hash->rcu, register_ftrace_direct_cb);
+
+	if (filter_hash)
+		free_ftrace_hash(filter_hash);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(unregister_ftrace_direct_hash);
+
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
 
 /**
-- 
2.50.1