On Tue, Feb 28, 2023 at 04:29:18PM -0800, Alexei Starovoitov wrote:

On Tue, Feb 28, 2023 at 9:07 AM David Vernet [off-list ref] wrote:

quoted

libbpf: prog 'on_lookup': failed to load: -13
libbpf: failed to load object 'cgrp_ls_recursion'
libbpf: failed to load BPF skeleton 'cgrp_ls_recursion': -13
test_recursion:FAIL:skel_open_and_load unexpected error: -13
#43/3    cgrp_local_storage/recursion:FAIL
#43      cgrp_local_storage:FAIL

All error logs:
test_cgrp_local_storage:PASS:join_cgroup /cgrp_local_storage 0 nsec
libbpf: prog 'on_lookup': BPF program load failed: Permission denied
libbpf: prog 'on_lookup': -- BEGIN PROG LOAD LOG --
reg type unsupported for arg#0 function on_lookup#16
0: R1=ctx(off=0,imm=0) R10=fp0
; struct task_struct *task = bpf_get_current_task_btf();
0: (85) call bpf_get_current_task_btf#158     ; R0_w=trusted_ptr_task_struct(off=0,imm=0)
1: (bf) r6 = r0                       ; R0_w=trusted_ptr_task_struct(off=0,imm=0) R6_w=trusted_ptr_task_struct(off=0,imm=0)
; bpf_cgrp_storage_delete(&map_a, task->cgroups->dfl_cgrp);
2: (79) r1 = *(u64 *)(r6 +2296)       ; R1_w=rcu_ptr_or_null_css_set(off=0,imm=0) R6_w=trusted_ptr_task_struct(off=0,imm=0)
; bpf_cgrp_storage_delete(&map_a, task->cgroups->dfl_cgrp);
3: (79) r2 = *(u64 *)(r1 +120)
R1 invalid mem access 'rcu_ptr_or_null_'

This one was tricky :)
Turned out btf_nested_type_is_trusted() was able to find
'cgroups' field in gcc compiled kernel and was failing on clang
compiled kernel because patch 2 did:
BTF_TYPE_SAFE_NESTED(struct task_struct) {
        const cpumask_t *cpus_ptr;
        struct css_set *cgroups;
};
instead of
BTF_TYPE_SAFE_NESTED(struct task_struct) {
        const cpumask_t *cpus_ptr;
        struct css_set __rcu *cgroups;
};
The missing tag was causing a miscompare.

Ahh, sorry I missed that in review. Once your patch set lands I'll add a
very loud comment here so that it's not missed in the future.

Something to keep in mind.
This ugliness will go away once GCC supports btf tag.

Looking forward to that day.

Given that you'll apply that fix to [0] here's my stamp for this patch:

Acked-by: David Vernet <void@manifault.com>

[0]: https://lore.kernel.org/all/20230228040121.94253-3-alexei.starovoitov@gmail.com/ (local)