linux-kernel - [RFC 09/10] bpf: Remove ftrace_ops from bpf

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Message-ID: <20250729102813.1531457-10-jolsa@kernel.org>
Date: Tue, 29 Jul 2025 12:28:12 +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 09/10] bpf: Remove ftrace_ops from bpf_trampoline object

We no longer need ftrace_ops in each bpf_trampoline object,
we can manage with just single ftrace_ops for all direct
trampoline attachments.

Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 include/linux/bpf.h     |  1 -
 kernel/bpf/trampoline.c | 34 ++++++++++------------------------
 2 files changed, 10 insertions(+), 25 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index c14bde400d97..bad29fe38a12 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1257,7 +1257,6 @@ struct bpf_trampoline {
 	struct hlist_node hlist_key;
 	/* hlist for trampoline_ip_table */
 	struct hlist_node hlist_ip;
-	struct ftrace_ops *fops;
 	/* serializes access to fields of this trampoline */
 	struct mutex mutex;
 	refcount_t refcnt;
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 398c1a722d83..e6a0e7b20bb6 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -175,16 +175,6 @@ static struct bpf_trampoline *bpf_trampoline_lookup(u64 key, unsigned long ip)
 	tr = kzalloc(sizeof(*tr), GFP_KERNEL);
 	if (!tr)
 		goto out;
-#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
-	tr->fops = kzalloc(sizeof(struct ftrace_ops), GFP_KERNEL);
-	if (!tr->fops) {
-		kfree(tr);
-		tr = NULL;
-		goto out;
-	}
-	tr->fops->private = tr;
-	tr->fops->ops_func = bpf_tramp_ftrace_ops_func;
-#endif
 
 	tr->key = key;
 	tr->ip = ip;
@@ -202,13 +192,19 @@ static struct bpf_trampoline *bpf_trampoline_lookup(u64 key, unsigned long ip)
 	return tr;
 }
 
+struct ftrace_ops direct_ops = {
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+       .ops_func = bpf_tramp_ftrace_ops_func,
+#endif
+};
+
 static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
 {
 	void *ip = tr->func.addr;
 	int ret;
 
 	if (tr->func.ftrace_managed)
-		ret = unregister_ftrace_direct(tr->fops, (unsigned long) ip, (long)old_addr, false);
+		ret = unregister_ftrace_direct(&direct_ops, (unsigned long) ip, (long)old_addr, false);
 	else
 		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL);
 
@@ -222,7 +218,7 @@ static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_ad
 	int ret;
 
 	if (tr->func.ftrace_managed) {
-		ret = modify_ftrace_direct(tr->fops, (unsigned long) ip, (long)new_addr, lock_direct_mutex);
+		ret = modify_ftrace_direct(&direct_ops, (unsigned long) ip, (long)new_addr, lock_direct_mutex);
 	} else {
 		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr);
 	}
@@ -237,14 +233,11 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
 	int ret;
 
 	faddr = ftrace_location((unsigned long)ip);
-	if (faddr) {
-		if (!tr->fops)
-			return -ENOTSUPP;
+	if (faddr)
 		tr->func.ftrace_managed = true;
-	}
 
 	if (tr->func.ftrace_managed) {
-		ret = register_ftrace_direct(tr->fops, (unsigned long)ip, (long)new_addr);
+		ret = register_ftrace_direct(&direct_ops, (unsigned long)ip, (long)new_addr);
 	} else {
 		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);
 	}
@@ -502,9 +495,6 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
 		 * BPF_TRAMP_F_SHARE_IPMODIFY is set, we can generate the
 		 * trampoline again, and retry register.
 		 */
-		/* reset fops->func and fops->trampoline for re-register */
-		tr->fops->func = NULL;
-		tr->fops->trampoline = 0;
 
 		/* free im memory and reallocate later */
 		bpf_tramp_image_free(im);
@@ -885,10 +875,6 @@ void bpf_trampoline_put(struct bpf_trampoline *tr)
 	 */
 	hlist_del(&tr->hlist_key);
 	hlist_del(&tr->hlist_ip);
-	if (tr->fops) {
-		ftrace_free_filter(tr->fops);
-		kfree(tr->fops);
-	}
 	kfree(tr);
 out:
 	mutex_unlock(&trampoline_mutex);
-- 
2.50.1