linux-kernel - [PATCH v3] btf: warn but return no error for NULL btf from __register_btf_kfunc_id

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Message-Id: <20230701171447.56464-1-sj@kernel.org>
Date:   Sat,  1 Jul 2023 17:14:47 +0000
From:   SeongJae Park <sj@...nel.org>
To:     daniel@...earbox.net
Cc:     SeongJae Park <sj@...nel.org>, Alexander.Egorenkov@....com,
        ast@...nel.org, jolsa@...nel.org, martin.lau@...ux.dev,
        memxor@...il.com, olsajiri@...il.com, bpf@...r.kernel.org,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3] 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/20220219082037.ow2kbq5brktf4f2u@apollo.legion/

Reported-by: Alexander Egorenkov <Alexander.Egorenkov@....com>
Link: https://lore.kernel.org/bpf/87y228q66f.fsf@oc8242746057.ibm.com/
Suggested-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
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@...r.kernel.org> # 5.18.x
Signed-off-by: SeongJae Park <sj@...nel.org>
Acked-by: Jiri Olsa <jolsa@...nel.org>
Signed-off-by: SeongJae Park <sj@...nel.org>
---

Changes from v2
(https://lore.kernel.org/bpf/20230628164611.83038-1-sj@kernel.org/)
- Keep the error for vmlinux case.
Changes from v1
(https://lore.kernel.org/all/20230626181120.7086-1-sj@kernel.org/)
- Fix Fixes: tag (Jiri Olsa)
- Add 'Acked-by: ' from Jiri Olsa

Notes
- This is a fix.  Hence, would better to merged into bpf tree, not
  bpf-next.
- This doesn't cleanly applied on 6.1.y.  I will send the backport to
  stable@ as soon as this is merged into the mainline.

 kernel/bpf/btf.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 29fe21099298..817204d53372 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7891,10 +7891,8 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
 			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_MODULES))
+			pr_warn("missing module BTF, cannot register kfuncs\n");
 		return 0;
 	}
 	if (IS_ERR(btf))
-- 
2.25.1