btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

__register_btf_kfunc_id_set() assumes .BTF to be part of the module's .ko file if CONFIG_DEBUG_INFO_BTF is enabled. If that's not the case, the function prints an error message and return an error. As a result, such modules cannot be loaded.

However, the section could be stripped out during a build process. It would be better to let the modules loaded, because their basic functionalities have no problem[1], though the BTF functionalities will not be supported. Make the function to lower the level of the message from error to warn, and return no error.

[1] https://lore.kernel.org/bpf/[email protected]/

Reported-by Alexander Egorenkov <[email protected]>

Link https://lore.kernel.org/bpf/[email protected]/ open here

Suggested-by Kumar Kartikeya Dwivedi <[email protected]>

Link https://lore.kernel.org/bpf/[email protected]/ open here

Fixes dee872e124e8 ("bpf: Populate kfunc BTF ID sets in struct btf")

Cc <[email protected]> # 5.17.x

Signed-off-by SeongJae Park <[email protected]>

---
 kernel/bpf/btf.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

kernel/bpf/btf.c +4 -8

index 6b682b8e4b50..d683f034996f 100644
@@ -7848,14 +7848,10 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
 
 	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_err("missing module BTF, cannot register kfuncs\n");
-			return -ENOENT;
-		}
+		if (!kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF))
+			pr_warn("missing vmlinux BTF, cannot register kfuncs\n");
+		if (kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES))
+			pr_warn("missing module BTF, cannot register kfuncs\n");
 		return 0;
 	}
 	if (IS_ERR(btf))

Signature · 1 line

2.25.1

Quoted 13 lines · SeongJae Park

__register_btf_kfunc_id_set() assumes .BTF to be part of the module's .ko file if CONFIG_DEBUG_INFO_BTF is enabled. If that's not the case, the function prints an error message and return an error. As a result, such modules cannot be loaded.

However, the section could be stripped out during a build process. It would be better to let the modules loaded, because their basic functionalities have no problem[1], though the BTF functionalities will not be supported. Make the function to lower the level of the message from error to warn, and return no error.

[1] https://lore.kernel.org/bpf/[email protected]/

Quoted 5 lines

Reported-by Alexander Egorenkov <[email protected]>

Link https://lore.kernel.org/bpf/[email protected]/ open here

Suggested-by Kumar Kartikeya Dwivedi <[email protected]>

Link https://lore.kernel.org/bpf/[email protected]/ open here

Fixes dee872e124e8 ("bpf: Populate kfunc BTF ID sets in struct btf")

should it be this one in Fixes instead?
c446fdacb10d bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF

other than that looks good

Acked-by Jiri Olsa <[email protected]>

jirka

Quoted 33 lines

Cc <[email protected]> # 5.17.x

Signed-off-by SeongJae Park <[email protected]>

---
 kernel/bpf/btf.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

kernel/bpf/btf.c +4 -8

index 6b682b8e4b50..d683f034996f 100644
@@ -7848,14 +7848,10 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
 
 	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_err("missing module BTF, cannot register kfuncs\n");
-			return -ENOENT;
-		}
+		if (!kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF))
+			pr_warn("missing vmlinux BTF, cannot register kfuncs\n");
+		if (kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES))
+			pr_warn("missing module BTF, cannot register kfuncs\n");
 		return 0;
 	}
 	if (IS_ERR(btf))

Signature · 1 line

2.25.1

Hi Jiri,

Quoted 14 lines · On Tue, 27 Jun 2023 18:20:39 +0200 Jiri Olsa <[email protected]> wrote:

Quoted 13 lines · SeongJae Park

__register_btf_kfunc_id_set() assumes .BTF to be part of the module's .ko file if CONFIG_DEBUG_INFO_BTF is enabled. If that's not the case, the function prints an error message and return an error. As a result, such modules cannot be loaded.

However, the section could be stripped out during a build process. It would be better to let the modules loaded, because their basic functionalities have no problem[1], though the BTF functionalities will not be supported. Make the function to lower the level of the message from error to warn, and return no error.

[1] https://lore.kernel.org/bpf/[email protected]/

Quoted 8 lines

Quoted 5 lines

Reported-by Alexander Egorenkov <[email protected]>

Link https://lore.kernel.org/bpf/[email protected]/ open here

Suggested-by Kumar Kartikeya Dwivedi <[email protected]>

Link https://lore.kernel.org/bpf/[email protected]/ open here

Fixes dee872e124e8 ("bpf: Populate kfunc BTF ID sets in struct btf")

should it be this one in Fixes instead?
c446fdacb10d bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF

The commit c446fdacb10d was trying to fix commit dee872e124e8, which this patch is claiming to fix, by relaxing the check. Nevertheless, it seems the check need to further relaxed, and therefore I wrote this patch.

For the reason, I was thinking this patch is directly fixing c446fdacb10d, but
is also fixing a problem originally introduced by dee872e124e8. Nevertheless,
as the dee872e124e8 also has the Fixes tag, I think your suggestion makes