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

[Eduard Zingerman]

On Sun, 2026-08-16 at 16:36 -0700, 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@xxxxxxxxxxxxxxxxxxxxx>
> > > ---
> > >  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?

I'm not being fair here. ksock series shown a real deficiency in
verier logic, matchers in Daniel's series were unstable.
Please disregard the above suggestion.