Subject: [PATCH bpf-next v2] bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF

From: Stanislav Fomichev <[email-masked]>
Date: Tue, 25 Jan 2022 16:13:40 -0800

Commit dee872e124e8 ("bpf: Populate kfunc BTF ID sets in struct btf")
breaks loading of some modules when CONFIG_DEBUG_INFO_BTF is not set.
register_btf_kfunc_id_set returns -ENOENT to the callers when
there is no module btf. Let's return 0 (success) instead to let
those modules work in !CONFIG_DEBUG_INFO_BTF cases.

Acked-by: Kumar Kartikeya Dwivedi <[email-masked]>
Fixes: dee872e124e8 ("bpf: Populate kfunc BTF ID sets in struct btf")
Signed-off-by: Stanislav Fomichev <[email-masked]>
---
 kernel/bpf/btf.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 57f5fd5af2f9..db8d6bb7f29f 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6740,8 +6740,19 @@ int register_btf_kfunc_id_set(enum bpf_prog_type prog_type,
 	int ret;
 
 	btf = btf_get_module_btf(kset->owner);
-	if (IS_ERR_OR_NULL(btf))
-		return btf ? PTR_ERR(btf) : -ENOENT;
+	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_err("missing module BTF, cannot register kfuncs\n");
+			return -ENOENT;
+		}
+		return 0;
+	}
+	if (IS_ERR(btf))
+		return PTR_ERR(btf);
 
 	hook = bpf_prog_type_to_kfunc_hook(prog_type);
 	ret = btf_populate_kfunc_set(btf, hook, kset);
-- 
2.35.0.rc0.227.g00780c9af4-goog