Merge branch 'bpf, btf: Add DEBUG_INFO_BTF checks for __register_bpf_struct_ops'

Geliang Tang says:

====================
bpf: Add DEBUG_INFO_BTF checks for __register_bpf_struct_ops

This patch set avoids module loading failure when the module
trying to register a struct_ops and the module has its btf section
stripped. This will then work similarly as module kfunc registration in
commit 3de4d22c ("bpf, btf: Warn but return no error for NULL btf from __register_btf_kfunc_id_set()")

v5:
 - drop CONFIG_MODULE_ALLOW_BTF_MISMATCH check as Martin suggested.

v4:
 - add a new patch to fix error checks for btf_get_module_btf.
 - rename the helper to check_btf_kconfigs.

v3:
 - fix this build error:
kernel/bpf/btf.c:7750:11: error: incomplete definition of type 'struct module'
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202402040934.Fph0XeEo-lkp@intel.com/

v2:
 - add register_check_missing_btf helper as Jiri suggested.
====================
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

kernel/bpf/btf.c

@@ -7738,6 +7738,17 @@ static struct btf *btf_get_module_btf(const struct module *module)
 	return btf;
 }
 
+static int check_btf_kconfigs(const struct module *module, const char *feature)
+{
+	if (!module && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
+		pr_err("missing vmlinux BTF, cannot register %s\n", feature);
+		return -ENOENT;
+	}
+	if (module && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES))
+		pr_warn("missing module BTF, cannot register %s\n", feature);
+	return 0;
+}
+
 BPF_CALL_4(bpf_btf_find_by_name_kind, char *, name, int, name_sz, u32, kind, int, flags)
 {
 	struct btf *btf = NULL;
@@ -8098,15 +8109,8 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
 	int ret, i;
 
 	btf = btf_get_module_btf(kset->owner);
-	if (!btf) {
-		if (!kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
-			pr_err("missing vmlinux BTF, cannot register kfuncs\n");
-			return -ENOENT;
-		}
-		if (kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES))
-			pr_warn("missing module BTF, cannot register kfuncs\n");
-		return 0;
-	}
+	if (!btf)
+		return check_btf_kconfigs(kset->owner, "kfunc");
 	if (IS_ERR(btf))
 		return PTR_ERR(btf);
 
@@ -8214,17 +8218,8 @@ int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors, u32 add_c
 	int ret;
 
 	btf = btf_get_module_btf(owner);
-	if (!btf) {
-		if (!owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
-			pr_err("missing vmlinux BTF, cannot register dtor kfuncs\n");
-			return -ENOENT;
-		}
-		if (owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES)) {
-			pr_err("missing module BTF, cannot register dtor kfuncs\n");
-			return -ENOENT;
-		}
-		return 0;
-	}
+	if (!btf)
+		return check_btf_kconfigs(owner, "dtor kfuncs");
 	if (IS_ERR(btf))
 		return PTR_ERR(btf);
 
@@ -8887,7 +8882,9 @@ int __register_bpf_struct_ops(struct bpf_struct_ops *st_ops)
 
 	btf = btf_get_module_btf(st_ops->owner);
 	if (!btf)
-		return -EINVAL;
+		return check_btf_kconfigs(st_ops->owner, "struct_ops");
+	if (IS_ERR(btf))
+		return PTR_ERR(btf);
 
 	log = kzalloc(sizeof(*log), GFP_KERNEL | __GFP_NOWARN);
 	if (!log) {