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

[Alexei Starovoitov]

On Tue, Nov 11, 2025 at 6:33 AM Saket Kumar Bhaskar <skb99@xxxxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > > ---
> > >  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.

alloc_htab_elem() is not inlined for me.
bpf_obj_free_fields() would be another option.