Re: [PATCH bpf-next v2] bpf: fix warning for crash_kexec

From: Yonghong Song <yonghong.song@linux.dev>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Hari Bathini <hbathini@linux.ibm.com>
Cc: bpf@vger.kernel.org, Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Kexec-ml <kexec@lists.infradead.org>, Baoquan He <bhe@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jiri Olsa <jolsa@kernel.org>, Stanislav Fomichev <sdf@google.com>
Subject: Re: [PATCH bpf-next v2] bpf: fix warning for crash_kexec
Date: Thu, 21 Mar 2024 16:30:11 -0700	[thread overview]
Message-ID: <0be8711f-31cb-4bfa-8501-4ad11e34b09a@linux.dev> (raw)
In-Reply-To: <CAEf4BzYpbQdjt+QBpbOPWr9tqErOhtMjb8gi_gZewubpUPgWGg@mail.gmail.com>

On 3/19/24 3:56 PM, Andrii Nakryiko wrote:
> On Tue, Mar 19, 2024 at 1:02 AM Hari Bathini <hbathini@linux.ibm.com> wrote:
>> With [1], crash dump specific code is moved out of CONFIG_KEXEC_CORE
>> and placed under CONFIG_CRASH_DUMP, where it is more appropriate.
>> And since CONFIG_KEXEC & !CONFIG_CRASH_DUMP build option is supported
>> with that, it led to the below warning:
>>
>>    "WARN: resolve_btfids: unresolved symbol crash_kexec"
>>
>> Fix it by using the appropriate #ifdef.
>>
>> [1] https://lore.kernel.org/all/20240124051254.67105-1-bhe@redhat.com/
>>
>> Acked-by: Baoquan He <bhe@redhat.com>
>> Fixes: 29fd9ae62910 ("crash: split crash dumping code out from kexec_core.c")
> I don't think either bpf or bpf-next have this commit just yet, so
> landing it in the bpf/bpf-next tree doesn't make much sense. It
> probably would be best to land it through the tree which does the
> CONFIG_KEXEC_CORE -> CONFIG_CRASH_DUMP change in kernel/Makefile.

With bpf-next, I found the config at kernel/Kconfig.kexec:

config CRASH_DUMP
         bool "kernel crash dumps"
         depends on ARCH_SUPPORTS_CRASH_DUMP
         select CRASH_CORE
         select KEXEC_CORE
         help

...

> pw-bot: cr
>
>> Acked-by: Jiri Olsa <jolsa@kernel.org>
>> Acked-by: Stanislav Fomichev <sdf@google.com>
>> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
>> ---
>>
>> Changes in v2:
>> * Updated changelog.
>> * Added Fixes and Acked-by tags.
>>
>>
>>   kernel/bpf/helpers.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
>> index a89587859571..449b9a5d3fe3 100644
>> --- a/kernel/bpf/helpers.c
>> +++ b/kernel/bpf/helpers.c
>> @@ -2548,7 +2548,7 @@ __bpf_kfunc void bpf_throw(u64 cookie)
>>   __bpf_kfunc_end_defs();
>>
>>   BTF_KFUNCS_START(generic_btf_ids)
>> -#ifdef CONFIG_KEXEC_CORE
>> +#ifdef CONFIG_CRASH_DUMP
>>   BTF_ID_FLAGS(func, crash_kexec, KF_DESTRUCTIVE)
>>   #endif
>>   BTF_ID_FLAGS(func, bpf_obj_new_impl, KF_ACQUIRE | KF_RET_NULL)
>> --
>> 2.44.0
>>