Re: [PATCH v2] btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

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On 6/28/23 6:46 PM, SeongJae Park wrote:
__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/20220219082037.ow2kbq5brktf4f2u@apollo.legion/

Reported-by: Alexander Egorenkov <Alexander.Egorenkov@xxxxxxx>
Link: https://lore.kernel.org/bpf/87y228q66f.fsf@xxxxxxxxxxxxxxxxxxxx/
Suggested-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
Link: https://lore.kernel.org/bpf/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
Fixes: c446fdacb10d ("bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF")
Cc: <stable@xxxxxxxxxxxxxxx> # 5.18.x
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>

I presume this one is targeted at bpf (rather than bpf-next) tree, right?

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 6b682b8e4b50..d683f034996f 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -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;
-		}

Why the above one needs to be changed? Do you also run into this case? vmlinux BTF
should be built-in in this case. I understand it's rather the one below for BTF +
modules instead, no?

-		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))





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