Re: [PATCH bpf] selftests/bpf: Fix a selftest compilation error with CONFIG_SMP=n

From: Yonghong Song <yhs@meta.com>
To: David Vernet <void@manifault.com>, Yonghong Song <yhs@fb.com>
Cc: bpf@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	kernel-team@fb.com, Martin KaFai Lau <martin.lau@kernel.org>,
	kernel test robot <lkp@intel.com>
Subject: Re: [PATCH bpf] selftests/bpf: Fix a selftest compilation error with CONFIG_SMP=n
Date: Mon, 12 Dec 2022 16:41:48 -0800	[thread overview]
Message-ID: <65954343-f164-4168-ea97-99ebf4f17445@meta.com> (raw)
In-Reply-To: <Y5fAHJTI742+jte7@maniforge.lan>

On 12/12/22 3:58 PM, David Vernet wrote:
> On Mon, Dec 12, 2022 at 03:46:17PM -0800, Yonghong Song wrote:
>> Kernel test robot reported bpf selftest build failure when CONFIG_SMP
>> is not set. The error message looks below:
>>
>>    >> progs/rcu_read_lock.c:256:34: error: no member named 'last_wakee' in 'struct task_struct'
>>               last_wakee = task->real_parent->last_wakee;
>>                            ~~~~~~~~~~~~~~~~~  ^
>>       1 error generated.
>>
>> When CONFIG_SMP is not set, the field 'last_wakee' is not available in struct
>> 'task_struct'. Hence the above compilation failure. To fix the issue, let us
>> choose another field 'group_leader' which is available regardless of
>> CONDFIG_SMP set or not.
> 
> s/CONDFIG_SMP/CONFIG_SMP
> 
>>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Signed-off-by: Yonghong Song <yhs@fb.com>
>> ---
>>   tools/testing/selftests/bpf/progs/rcu_read_lock.c      | 8 ++++----
>>   tools/testing/selftests/bpf/progs/task_kfunc_failure.c | 2 +-
>>   2 files changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/tools/testing/selftests/bpf/progs/rcu_read_lock.c b/tools/testing/selftests/bpf/progs/rcu_read_lock.c
>> index 125f908024d3..5cecbdbbb16e 100644
>> --- a/tools/testing/selftests/bpf/progs/rcu_read_lock.c
>> +++ b/tools/testing/selftests/bpf/progs/rcu_read_lock.c
>> @@ -288,13 +288,13 @@ int nested_rcu_region(void *ctx)
>>   SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
>>   int task_untrusted_non_rcuptr(void *ctx)
>>   {
>> -	struct task_struct *task, *last_wakee;
>> +	struct task_struct *task, *group_leader;
>>   
>>   	task = bpf_get_current_task_btf();
>>   	bpf_rcu_read_lock();
>> -	/* the pointer last_wakee marked as untrusted */
>> -	last_wakee = task->real_parent->last_wakee;
>> -	(void)bpf_task_storage_get(&map_a, last_wakee, 0, 0);
>> +	/* the pointer group_leader marked as untrusted */
>> +	group_leader = task->real_parent->group_leader;
>> +	(void)bpf_task_storage_get(&map_a, group_leader, 0, 0);
>>   	bpf_rcu_read_unlock();
>>   	return 0;
>>   }
>> diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c
>> index 87fa1db9d9b5..1b47b94dbca0 100644
>> --- a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c
>> +++ b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c
>> @@ -73,7 +73,7 @@ int BPF_PROG(task_kfunc_acquire_trusted_walked, struct task_struct *task, u64 cl
>>   	struct task_struct *acquired;
>>   
>>   	/* Can't invoke bpf_task_acquire() on a trusted pointer obtained from walking a struct. */
>> -	acquired = bpf_task_acquire(task->last_wakee);
>> +	acquired = bpf_task_acquire(task->group_leader);
> 
> Ah, I missed that you'd sent this out before I sent out [0]. Thanks for
> fixing this for me. I'm fine with just merging this patch and dropping
> [0] if it's easier for the maintainers.
> 
> [0]: https://lore.kernel.org/all/20221212235344.1563280-1-void@manifault.com/

I found the above as well since with the kernel-test-bot config, both
rcu_read_lock.c and task_kfunc_failure.c caused compilation errors.

Let me send another version by fixing the above CONFIG_SMP typo,
adding proper fix tags and adding your sign-off and ack.

Thanks!

> 
>>   	bpf_task_release(acquired);
>>   
>>   	return 0;
>> -- 
>> 2.30.2
>>