linux-kernel - [RFC 04/10] ftrace: Add modify_ftrace_direct

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Message-ID: <20250729102813.1531457-5-jolsa@kernel.org>
Date: Tue, 29 Jul 2025 12:28:07 +0200
From: Jiri Olsa <jolsa@...nel.org>
To: Steven Rostedt <rostedt@...nel.org>,
	Florent Revest <revest@...gle.com>,
	Mark Rutland <mark.rutland@....com>
Cc: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Menglong Dong <menglong8.dong@...il.com>
Subject: [RFC 04/10] ftrace: Add modify_ftrace_direct_hash function

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

The difference to current unregister_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@...nel.org>
---
 include/linux/ftrace.h |  6 +++++
 kernel/trace/ftrace.c  | 58 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 7ff6004498c0..8761765d9abc 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -528,6 +528,7 @@ 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);
+int modify_ftrace_direct_hash(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock);
 
 void ftrace_stub_direct_tramp(void);
 
@@ -565,6 +566,11 @@ int unregister_ftrace_direct_hash(struct ftrace_ops *ops, struct ftrace_hash *ha
 	return -ENODEV;
 }
 
+int modify_ftrace_direct_hash(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 d761237ec70f..755d5550ac44 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6440,6 +6440,64 @@ int unregister_ftrace_direct_hash(struct ftrace_ops *ops, struct ftrace_hash *ha
 }
 EXPORT_SYMBOL_GPL(unregister_ftrace_direct_hash);
 
+int modify_ftrace_direct_hash(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock)
+{
+	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 0;
+	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;
+
+	/*
+	 * 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);
+
+	/* 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;
+}
+EXPORT_SYMBOL_GPL(modify_ftrace_direct_hash);
+
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
 
 /**
-- 
2.50.1