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

[Yonghong Song <yhs@xxxxxxxx>]

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@xxxxxxxxx>
> > Signed-off-by: Yonghong Song <yhs@xxxxxx>
> > ---
> >   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@xxxxxxxxxxxxx/

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