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

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

[Saket Kumar Bhaskar]

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");
 out:
 	htab_update__destroy(skel);
 }
-- 
2.51.0

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

[Alexei Starovoitov]

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

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

[Saket Kumar Bhaskar]

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

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@linux.ibm.com> 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@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.

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

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

[Saket Kumar Bhaskar]

On Tue, Nov 11, 2025 at 10:35:39AM -0800, Alexei Starovoitov wrote:
> On Tue, Nov 11, 2025 at 6:33 AM Saket Kumar Bhaskar <skb99@linux.ibm.com> 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@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.
> 
> alloc_htab_elem() is not inlined for me.
> bpf_obj_free_fields() would be another option.
Since alloc_htab_elem() is a static function, wouldn’t its
inlining behavior be compiler-dependent?

static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
                                         void *value, u32 key_size, u32 hash,
                                         bool percpu, bool onallcpus,
                                         struct htab_elem *old_elem)

When the fentry program is instead attached to bpf_obj_free_fields(),
the bpf_map_update_elem() call returns 0 rather than -EDEADLK, 
because bpf_obj_free_fields() is not invoked in the bpf_map_update_elem() 
re-entrancy path:

./test_progs -t htab_update/reenter_update -v
bpf_testmod.ko is already unloaded.
Loading bpf_testmod.ko...
Successfully loaded bpf_testmod.ko.
test_reenter_update:PASS:htab_update__open 0 nsec
test_reenter_update:PASS:htab_update__load 0 nsec
test_reenter_update:PASS:htab_update__attach 0 nsec
test_reenter_update:PASS:add element 0 nsec
test_reenter_update:FAIL:no reentrancy unexpected no reentrancy: actual 0 != expected -35
#143/1   htab_update/reenter_update:FAIL
#143     htab_update:FAIL
Summary: 0/0 PASSED, 0 SKIPPED, 1 FAILED
Successfully unloaded bpf_testmod.ko.

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

[Alexei Starovoitov]

On Wed, Nov 12, 2025 at 7:08 AM Saket Kumar Bhaskar <skb99@linux.ibm.com> wrote:
>
> On Tue, Nov 11, 2025 at 10:35:39AM -0800, Alexei Starovoitov wrote:
> > On Tue, Nov 11, 2025 at 6:33 AM Saket Kumar Bhaskar <skb99@linux.ibm.com> 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@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.
> >
> > alloc_htab_elem() is not inlined for me.
> > bpf_obj_free_fields() would be another option.
> Since alloc_htab_elem() is a static function, wouldn’t its
> inlining behavior be compiler-dependent?

of course. Just like lookup_elem_raw(), but alloc is much bigger
and less likely to be inlined.

> static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
>                                          void *value, u32 key_size, u32 hash,
>                                          bool percpu, bool onallcpus,
>                                          struct htab_elem *old_elem)
>
> When the fentry program is instead attached to bpf_obj_free_fields(),
> the bpf_map_update_elem() call returns 0 rather than -EDEADLK,
> because bpf_obj_free_fields() is not invoked in the bpf_map_update_elem()
> re-entrancy path:

Then make it so. Think what you need to do to make
check_and_free_fields() call it.