Re: [PATCH bpf-next v2 2/2] selftests/bpf: Cover mixed arena and stack atomics

[Vineet Gupta <vineet.gupta@linux.dev>]

On 8/18/26 12:56 PM, Eduard Zingerman wrote:
> On Tue, 2026-08-18 at 12:35 -0700, Vineet Gupta wrote:
>> On 8/16/26 4:36 PM, Eduard Zingerman wrote:
>>> On Sun, 2026-08-16 at 16:17 -0700, Eduard Zingerman wrote:
>>>> On Sun, 2026-08-16 at 10:56 +0000, Yiyang Chen wrote:
>>>>> Add a verifier test with one atomic RMW instruction reached through
>>>>> PTR_TO_ARENA and PTR_TO_STACK paths. The verifier must reject the
>>>>> shared instruction with the existing incompatible-pointer diagnostic.
>>>>>
>>>>> Signed-off-by: Yiyang Chen <chenyy23@mails.tsinghua.edu.cn>
>>>>> ---
>>>>>    tools/testing/selftests/bpf/progs/verifier_arena.c | 39 ++++++++++++++++++++++
>>>>>    1 file changed, 39 insertions(+)
>>>>>
>>>>> diff --git a/tools/testing/selftests/bpf/progs/verifier_arena.c b/tools/testing/selftests/bpf/progs/verifier_arena.c
>>>>> index b241bbcf54a8a..b22bab33301ab 100644
>>>>> --- a/tools/testing/selftests/bpf/progs/verifier_arena.c
>>>>> +++ b/tools/testing/selftests/bpf/progs/verifier_arena.c
>>>>> @@ -637,6 +637,45 @@ int non_arena_ptr_add_to_arena_ptr(void *ctx)
>>>>>    
>>>>>    #endif
>>>>>    
>>>>> +static const struct bpf_insn addr_space_cast_insn = {
>>>>> +	.code = 0xbf,
>>>>> +	.dst_reg = BPF_REG_7,
>>>>> +	.src_reg = BPF_REG_7,
>>>>> +	.off = 1,
>>>>> +	.imm = 1,
>>>>> +};
>>>>> +
>>>>> +SEC("socket")
>>>>> +__description("arena and stack atomic at the same instruction")
>>>>> +__failure __msg("same insn cannot be used with different pointers")
>>>>> +__arch_x86_64
>>>>> +__load_if_JITed()
>>>>> +__naked void mixed_arena_stack_atomic(void)
>>>>> +{
>>>>> +	asm volatile ("					\
>>>>> +	r1 = %[arena] ll;				\
>>>>> +	r6 = r10;					\
>>>>> +	r6 += -8;					\
>>>>> +	r9 = 0;					\
>>>>> +	*(u64 *)(r6 + 0) = r9;			\
>>>>> +	r7 = 8192;					\
>>>>> +	.8byte %[addr_space_cast];			\
>>>> I'm going to fix this to:
>>>>
>>>> 	r7 = addr_space_cast(r7, 0, 1);			\
>>>>
>>>> as in the test case above.
>>>> Waiting for CI [1].
>>>>
>>>> [1] https://github.com/kernel-patches/bpf/pull/13325
>>> A...and it requires another exception for GCC-BPF:
>>> https://github.com/kernel-patches/bpf/blob/bpf-next_base/ci/vmtest/configs/DENYLIST.test_progs-bpf_gcc
>>>
>>> Ihor, it's a third time GCC-BPF strikes this weekend.
>>> What do people think about downgrading it to may-fail until the
>>> DENYLIST decreases to something reasonable?
>> While bpf-gcc is improving, slowly, we can in parallel do alittle better
>> on test hygiene as well. In this case by correctly bracketing the tests
>> with _BPF_FEATURE_XXX.
> Yes, that's what I ended up doing. Should have paid attention to the
> #if .. #endif bracket used by the textually preceding test.
> Sorry for lashing out.

No worries and I can sympathize with frustrations when someone's s*it is 
not together and others have to suffer

-Vineet