[PATCH bpf-next 07/25] ftrace: add reset_ftrace_direct_ips

[Menglong Dong <menglong8.dong@gmail.com>]

For now, we can change the address of a direct ftrace_ops with
modify_ftrace_direct(). However, we can't change the functions to filter
for a direct ftrace_ops. Therefore, we introduce the function
reset_ftrace_direct_ips() to do such things, and this function will reset
the functions to filter for a direct ftrace_ops.

This function do such thing in following steps:

1. filter out the new functions from ips that don't exist in the
   ops->func_hash->filter_hash and add them to the new hash.
2. add all the functions in the new ftrace_hash to direct_functions by
   ftrace_direct_update().
3. reset the functions to filter of the ftrace_ops to the ips with
   ftrace_set_filter_ips().
4. remove the functions that in the old ftrace_hash, but not in the new
   ftrace_hash from direct_functions.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
---
 include/linux/ftrace.h |  7 ++++
 kernel/trace/ftrace.c  | 75 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index fbabc3d848b3..40727d3f125d 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -526,6 +526,8 @@ int modify_ftrace_direct_nolock(struct ftrace_ops *ops, unsigned long addr);
 
 void ftrace_stub_direct_tramp(void);
 
+int reset_ftrace_direct_ips(struct ftrace_ops *ops, unsigned long *ips,
+			    unsigned int cnt);
 #else
 struct ftrace_ops;
 static inline unsigned long ftrace_find_rec_direct(unsigned long ip)
@@ -549,6 +551,11 @@ static inline int modify_ftrace_direct_nolock(struct ftrace_ops *ops, unsigned l
 {
 	return -ENODEV;
 }
+static inline int reset_ftrace_direct_ips(struct ftrace_ops *ops, unsigned long *ips,
+					  unsigned int cnt)
+{
+	return -ENODEV;
+}
 
 /*
  * This must be implemented by the architecture.
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a1028942e743..0befb4c93e89 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6181,6 +6181,81 @@ int modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
 	return err;
 }
 EXPORT_SYMBOL_GPL(modify_ftrace_direct);
+
+/* reset the ips for a direct ftrace (add or remove) */
+int reset_ftrace_direct_ips(struct ftrace_ops *ops, unsigned long *ips,
+			    unsigned int cnt)
+{
+	struct ftrace_hash *hash, *free_hash;
+	struct ftrace_func_entry *entry, *del;
+	unsigned long ip;
+	int err, size;
+
+	if (check_direct_multi(ops))
+		return -EINVAL;
+	if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
+		return -EINVAL;
+
+	mutex_lock(&direct_mutex);
+	hash = alloc_ftrace_hash(FTRACE_HASH_DEFAULT_BITS);
+	if (!hash) {
+		err = -ENOMEM;
+		goto out_unlock;
+	}
+
+	/* find out the new functions from ips and add to hash */
+	for (int i = 0; i < cnt; i++) {
+		ip = ftrace_location(ips[i]);
+		if (!ip) {
+			err = -ENOENT;
+			goto out_unlock;
+		}
+		if (__ftrace_lookup_ip(ops->func_hash->filter_hash, ip))
+			continue;
+		err = __ftrace_match_addr(hash, ip, 0);
+		if (err)
+			goto out_unlock;
+	}
+
+	free_hash = direct_functions;
+	/* add the new ips to direct hash. */
+	err = ftrace_direct_update(hash, ops->direct_call);
+	if (err)
+		goto out_unlock;
+
+	if (free_hash && free_hash != EMPTY_HASH)
+		call_rcu_tasks(&free_hash->rcu, register_ftrace_direct_cb);
+
+	free_ftrace_hash(hash);
+	hash = alloc_and_copy_ftrace_hash(FTRACE_HASH_DEFAULT_BITS,
+					  ops->func_hash->filter_hash);
+	if (!hash) {
+		err = -ENOMEM;
+		goto out_unlock;
+	}
+	err = ftrace_set_filter_ips(ops, ips, cnt, 0, 1);
+
+	/* remove the entries that don't exist in our filter_hash anymore
+	 * from the direct_functions.
+	 */
+	size = 1 << hash->size_bits;
+	for (int i = 0; i < size; i++) {
+		hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
+			if (__ftrace_lookup_ip(ops->func_hash->filter_hash, entry->ip))
+				continue;
+			del = __ftrace_lookup_ip(direct_functions, entry->ip);
+			if (del && del->direct == ops->direct_call) {
+				remove_hash_entry(direct_functions, del);
+				kfree(del);
+			}
+		}
+	}
+out_unlock:
+	mutex_unlock(&direct_mutex);
+	if (hash)
+		free_ftrace_hash(hash);
+	return err;
+}
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
 
 /**
-- 
2.39.5