Re: [PATCH bpf-next] selftests/bpf: Fix htab_update/reenter_update selftest failure

[Saket Kumar Bhaskar <skb99@linux.ibm.com>]

On Thu, Nov 06, 2025 at 09:15:39AM -0800, Alexei Starovoitov wrote:
> On Wed, Nov 5, 2025 at 9:26 PM Saket Kumar Bhaskar <skb99@linux.ibm.com> wrote:
> >
> > Since commit 31158ad02ddb ("rqspinlock: Add deadlock detection and recovery")
> > the updated path on re-entrancy now reports deadlock via
> > -EDEADLK instead of the previous -EBUSY.
> >
> > The selftest is updated to align with expected errno
> > with the kernel’s current behavior.
> >
> > Signed-off-by: Saket Kumar Bhaskar <skb99@linux.ibm.com>
> > ---
> >  tools/testing/selftests/bpf/prog_tests/htab_update.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/htab_update.c b/tools/testing/selftests/bpf/prog_tests/htab_update.c
> > index 2bc85f4814f4..98d52bb1446f 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/htab_update.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/htab_update.c
> > @@ -40,7 +40,7 @@ static void test_reenter_update(void)
> >         if (!ASSERT_OK(err, "add element"))
> >                 goto out;
> >
> > -       ASSERT_EQ(skel->bss->update_err, -EBUSY, "no reentrancy");
> > +       ASSERT_EQ(skel->bss->update_err, -EDEADLK, "no reentrancy");
> 
> Makes sense, but looks like the test was broken for quite some time.
> It fails with
>         /* lookup_elem_raw() may be inlined and find_kernel_btf_id()
> will return -ESRCH */
>         bpf_program__set_autoload(skel->progs.lookup_elem_raw, true);
>         err = htab_update__load(skel);
>         if (!ASSERT_TRUE(!err || err == -ESRCH, "htab_update__load") || err)
> 
> before reaching deadlk check.
> Pls make it more robust.
> __pcpu_freelist_pop() might be better alternative then lookup_elem_raw().
> 
> pw-bot: cr

Hi Alexei,

I tried for __pcpu_freelist_pop, looks like it is not good candidate to
attach fentry for, as it is non traceable:

trace_kprobe: Could not probe notrace function __pcpu_freelist_pop

I wasn't able to find any other function for this.

Thanks
Saket