Message-ID: <20250801071622.63dc9b78@gandalf.local.home>
Date: Fri, 1 Aug 2025 07:16:22 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>, bpf@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
 <andrii@...nel.org>, Jiri Olsa <jolsa@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu
 <song@...nel.org>, KP Singh <kpsingh@...nel.org>
Subject: [PATCH] btf: Simplify BTF logic with use of __free(btf_put)

From: Steven Rostedt <rostedt@...dmis.org>

Several functions need to call btf_put() on the btf pointer before it
returns leading to using "goto" branches to jump to the end to call
btf_put(btf). This can be simplified by introducing DEFINE_FREE() to allow
functions to define the btf descriptor with:

   struct btf *btf __free(btf_put) = NULL;

Then the btf descriptor will always have btf_put() called on it if it
isn't NULL or ERR before exiting the function.

Where needed, no_free_ptr(btf) is used to assign the btf descriptor to a
pointer that will be used outside the function.

Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 include/linux/btf.h         |  4 +++
 kernel/bpf/btf.c            | 56 +++++++++++--------------------------
 kernel/trace/trace_btf.c    | 15 +++++-----
 kernel/trace/trace_output.c |  8 ++----
 4 files changed, 31 insertions(+), 52 deletions(-)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index b2983706292f..e118c69c4996 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -8,6 +8,7 @@
 #include <linux/bpfptr.h>
 #include <linux/bsearch.h>
 #include <linux/btf_ids.h>
+#include <linux/cleanup.h>
 #include <uapi/linux/btf.h>
 #include <uapi/linux/bpf.h>
 
@@ -150,6 +151,9 @@ struct btf *btf_get_by_fd(int fd);
 int btf_get_info_by_fd(const struct btf *btf,
 		       const union bpf_attr *attr,
 		       union bpf_attr __user *uattr);
+
+DEFINE_FREE(btf_put, struct btf *, if (!IS_ERR_OR_NULL(_T)) btf_put(_T))
+
 /* Figure out the size of a type_id.  If type_id is a modifier
  * (e.g. const), it will be resolved to find out the type with size.
  *
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 1d2cf898e21e..480657912c96 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3788,7 +3788,7 @@ static int btf_parse_kptr(const struct btf *btf, struct btf_field *field,
 	/* If a matching btf type is found in kernel or module BTFs, kptr_ref
 	 * is that BTF, otherwise it's program BTF
 	 */
-	struct btf *kptr_btf;
+	struct btf *kptr_btf __free(btf_put) = NULL;
 	int ret;
 	s32 id;
 
@@ -3827,23 +3827,17 @@ static int btf_parse_kptr(const struct btf *btf, struct btf_field *field,
 		 * the same time.
 		 */
 		dtor_btf_id = btf_find_dtor_kfunc(kptr_btf, id);
-		if (dtor_btf_id < 0) {
-			ret = dtor_btf_id;
-			goto end_btf;
-		}
+		if (dtor_btf_id < 0)
+			return dtor_btf_id;
 
 		dtor_func = btf_type_by_id(kptr_btf, dtor_btf_id);
-		if (!dtor_func) {
-			ret = -ENOENT;
-			goto end_btf;
-		}
+		if (!dtor_func)
+			return -ENOENT;
 
 		if (btf_is_module(kptr_btf)) {
 			mod = btf_try_get_module(kptr_btf);
-			if (!mod) {
-				ret = -ENXIO;
-				goto end_btf;
-			}
+			if (!mod)
+				return -ENXIO;
 		}
 
 		/* We already verified dtor_func to be btf_type_is_func
@@ -3860,13 +3854,11 @@ static int btf_parse_kptr(const struct btf *btf, struct btf_field *field,
 
 found_dtor:
 	field->kptr.btf_id = id;
-	field->kptr.btf = kptr_btf;
+	field->kptr.btf = no_free_ptr(kptr_btf);
 	field->kptr.module = mod;
 	return 0;
 end_mod:
 	module_put(mod);
-end_btf:
-	btf_put(kptr_btf);
 	return ret;
 }
 
@@ -8699,7 +8691,7 @@ u32 *btf_kfunc_is_modify_return(const struct btf *btf, u32 kfunc_btf_id,
 static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
 				       const struct btf_kfunc_id_set *kset)
 {
-	struct btf *btf;
+	struct btf *btf __free(btf_put) = NULL;
 	int ret, i;
 
 	btf = btf_get_module_btf(kset->owner);
@@ -8712,14 +8704,10 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
 		ret = btf_check_kfunc_protos(btf, btf_relocate_id(btf, kset->set->pairs[i].id),
 					     kset->set->pairs[i].flags);
 		if (ret)
-			goto err_out;
+			return ret;
 	}
 
-	ret = btf_populate_kfunc_set(btf, hook, kset);
-
-err_out:
-	btf_put(btf);
-	return ret;
+	return btf_populate_kfunc_set(btf, hook, kset);
 }
 
 /* This function must be invoked only from initcalls/module init functions */
@@ -8807,7 +8795,7 @@ int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors, u32 add_c
 				struct module *owner)
 {
 	struct btf_id_dtor_kfunc_tab *tab;
-	struct btf *btf;
+	struct btf *btf __free(btf_put) = NULL;
 	u32 tab_cnt, i;
 	int ret;
 
@@ -8873,7 +8861,6 @@ int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors, u32 add_c
 end:
 	if (ret)
 		btf_free_dtor_kfunc_tab(btf);
-	btf_put(btf);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(register_btf_id_dtor_kfuncs);
@@ -9484,9 +9471,8 @@ bpf_struct_ops_find(struct btf *btf, u32 type_id)
 
 int __register_bpf_struct_ops(struct bpf_struct_ops *st_ops)
 {
-	struct bpf_verifier_log *log;
-	struct btf *btf;
-	int err = 0;
+	struct bpf_verifier_log *log __free(kfree) = NULL;
+	struct btf *btf __free(btf_put) = NULL;
 
 	btf = btf_get_module_btf(st_ops->owner);
 	if (!btf)
@@ -9495,20 +9481,12 @@ int __register_bpf_struct_ops(struct bpf_struct_ops *st_ops)
 		return PTR_ERR(btf);
 
 	log = kzalloc(sizeof(*log), GFP_KERNEL | __GFP_NOWARN);
-	if (!log) {
-		err = -ENOMEM;
-		goto errout;
-	}
+	if (!log)
+		return -ENOMEM;
 
 	log->level = BPF_LOG_KERNEL;
 
-	err = btf_add_struct_ops(btf, st_ops, log);
-
-errout:
-	kfree(log);
-	btf_put(btf);
-
-	return err;
+	return btf_add_struct_ops(btf, st_ops, log);
 }
 EXPORT_SYMBOL_GPL(__register_bpf_struct_ops);
 #endif
diff --git a/kernel/trace/trace_btf.c b/kernel/trace/trace_btf.c
index 5bbdbcbbde3c..1c9111ab538b 100644
--- a/kernel/trace/trace_btf.c
+++ b/kernel/trace/trace_btf.c
@@ -13,26 +13,25 @@
 const struct btf_type *btf_find_func_proto(const char *func_name, struct btf **btf_p)
 {
 	const struct btf_type *t;
+	struct btf *btf __free(btf_put) = NULL;
 	s32 id;
 
-	id = bpf_find_btf_id(func_name, BTF_KIND_FUNC, btf_p);
+	id = bpf_find_btf_id(func_name, BTF_KIND_FUNC, &btf);
 	if (id < 0)
 		return NULL;
 
 	/* Get BTF_KIND_FUNC type */
-	t = btf_type_by_id(*btf_p, id);
+	t = btf_type_by_id(btf, id);
 	if (!t || !btf_type_is_func(t))
-		goto err;
+		return NULL;
 
 	/* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
-	t = btf_type_by_id(*btf_p, t->type);
+	t = btf_type_by_id(btf, t->type);
 	if (!t || !btf_type_is_func_proto(t))
-		goto err;
+		return NULL;
 
+	*btf_p = no_free_ptr(btf);
 	return t;
-err:
-	btf_put(*btf_p);
-	return NULL;
 }
 
 /*
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 0b3db02030a7..c11adfa83d5c 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -698,7 +698,7 @@ void print_function_args(struct trace_seq *s, unsigned long *args,
 	const char *param_name;
 	char name[KSYM_NAME_LEN];
 	unsigned long arg;
-	struct btf *btf;
+	struct btf *btf __free(btf_put) = NULL;
 	s32 tid, nr = 0;
 	int a, p, x;
 
@@ -716,7 +716,7 @@ void print_function_args(struct trace_seq *s, unsigned long *args,
 
 	param = btf_get_func_param(t, &nr);
 	if (!param)
-		goto out_put;
+		goto out;
 
 	for (a = 0, p = 0; p < nr; a++, p++) {
 		if (p)
@@ -756,7 +756,7 @@ void print_function_args(struct trace_seq *s, unsigned long *args,
 				trace_seq_putc(s, ':');
 				if (++a == FTRACE_REGS_MAX_ARGS) {
 					trace_seq_puts(s, "...]");
-					goto out_put;
+					goto out;
 				}
 				trace_seq_printf(s, "0x%lx", args[a]);
 			}
@@ -764,8 +764,6 @@ void print_function_args(struct trace_seq *s, unsigned long *args,
 			break;
 		}
 	}
-out_put:
-	btf_put(btf);
 out:
 	trace_seq_printf(s, ")");
 }
-- 
2.47.2

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