Re: [PATCH bpf-next 2/2] selftests/bpf: Add a local kptr test with no special fields

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On 8/23/23 6:56 PM, Yonghong Song wrote:
> Add a local kptr test with no special fields in the struct. Without the
> previous patch, the following warning will hit:
> 
>   [   44.683877] WARNING: CPU: 3 PID: 485 at kernel/bpf/syscall.c:660 bpf_obj_free_fields+0x220/0x240
>   [   44.684640] Modules linked in: bpf_testmod(OE)
>   [   44.685044] CPU: 3 PID: 485 Comm: kworker/u8:5 Tainted: G           OE      6.5.0-rc5-01703-g260d855e9b90 #248
>   [   44.685827] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
>   [   44.686693] Workqueue: events_unbound bpf_map_free_deferred
>   [   44.687297] RIP: 0010:bpf_obj_free_fields+0x220/0x240
>   [   44.687775] Code: e8 55 17 1f 00 49 8b 74 24 08 4c 89 ef e8 e8 14 05 00 e8 a3 da e2 ff e9 55 fe ff ff 0f 0b e9 4e fe ff
>                        ff 0f 0b e9 47 fe ff ff <0f> 0b e8 d9 d9 e2 ff 31 f6 eb d5 48 83 c4 10 5b 41 5c e
>   [   44.689353] RSP: 0018:ffff888106467cb8 EFLAGS: 00010246
>   [   44.689806] RAX: 0000000000000000 RBX: ffff888112b3a200 RCX: 0000000000000001
>   [   44.690433] RDX: 0000000000000000 RSI: dffffc0000000000 RDI: ffff8881128ad988
>   [   44.691094] RBP: 0000000000000002 R08: ffffffff81370bd0 R09: 1ffff110216231a5
>   [   44.691643] R10: dffffc0000000000 R11: ffffed10216231a6 R12: ffff88810d68a488
>   [   44.692245] R13: ffff88810767c288 R14: ffff88810d68a400 R15: ffff88810d68a418
>   [   44.692829] FS:  0000000000000000(0000) GS:ffff8881f7580000(0000) knlGS:0000000000000000
>   [   44.693484] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   [   44.693964] CR2: 000055c7f2afce28 CR3: 000000010fee4002 CR4: 0000000000370ee0
>   [   44.694513] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>   [   44.695102] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>   [   44.695747] Call Trace:
>   [   44.696001]  <TASK>
>   [   44.696183]  ? __warn+0xfe/0x270
>   [   44.696447]  ? bpf_obj_free_fields+0x220/0x240
>   [   44.696817]  ? report_bug+0x220/0x2d0
>   [   44.697180]  ? handle_bug+0x3d/0x70
>   [   44.697507]  ? exc_invalid_op+0x1a/0x50
>   [   44.697887]  ? asm_exc_invalid_op+0x1a/0x20
>   [   44.698282]  ? btf_find_struct_meta+0xd0/0xd0
>   [   44.698634]  ? bpf_obj_free_fields+0x220/0x240
>   [   44.699027]  ? bpf_obj_free_fields+0x1e2/0x240
>   [   44.699414]  array_map_free+0x1a3/0x260
>   [   44.699763]  bpf_map_free_deferred+0x7b/0xe0
>   [   44.700154]  process_one_work+0x46d/0x750
>   [   44.700523]  worker_thread+0x49e/0x900
>   [   44.700892]  ? pr_cont_work+0x270/0x270
>   [   44.701224]  kthread+0x1ae/0x1d0
>   [   44.701516]  ? kthread_blkcg+0x50/0x50
>   [   44.701860]  ret_from_fork+0x34/0x50
>   [   44.702178]  ? kthread_blkcg+0x50/0x50
>   [   44.702508]  ret_from_fork_asm+0x11/0x20
>   [   44.702880]  </TASK>
> 
> With the previous patch, there is no warnings.
> 
> Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
> ---
>  .../bpf/prog_tests/local_kptr_stash.c         | 25 ++++++++++++++++-
>  .../selftests/bpf/progs/local_kptr_stash.c    | 28 +++++++++++++++++++
>  2 files changed, 52 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/local_kptr_stash.c b/tools/testing/selftests/bpf/prog_tests/local_kptr_stash.c
> index 158616c94658..4225108b8e4d 100644
> --- a/tools/testing/selftests/bpf/prog_tests/local_kptr_stash.c
> +++ b/tools/testing/selftests/bpf/prog_tests/local_kptr_stash.c
> @@ -27,6 +27,27 @@ static void test_local_kptr_stash_simple(void)
>  	local_kptr_stash__destroy(skel);
>  }
>  
> +static void test_local_kptr_stash_simple_2(void)
> +{
> +	LIBBPF_OPTS(bpf_test_run_opts, opts,
> +		    .data_in = &pkt_v4,
> +		    .data_size_in = sizeof(pkt_v4),
> +		    .repeat = 1,
> +	);
> +	struct local_kptr_stash *skel;
> +	int ret;
> +
> +	skel = local_kptr_stash__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "local_kptr_stash__open_and_load"))
> +		return;
> +
> +	ret = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.stash_rb_nodes_2), &opts);
> +	ASSERT_OK(ret, "local_kptr_stash_add_nodes run");
> +	ASSERT_OK(opts.retval, "local_kptr_stash_add_nodes retval");
> +
> +	local_kptr_stash__destroy(skel);
> +}
> +
>  static void test_local_kptr_stash_unstash(void)
>  {
>  	LIBBPF_OPTS(bpf_test_run_opts, opts,
> @@ -59,8 +80,10 @@ static void test_local_kptr_stash_fail(void)
>  
>  void test_local_kptr_stash(void)
>  {
> -	if (test__start_subtest("local_kptr_stash_simple"))
> +	if (test__start_subtest("local_kptr_stash_simple_yes_special_field"))
>  		test_local_kptr_stash_simple();
> +	if (test__start_subtest("local_kptr_stash_simple_no_special_field"))
> +		test_local_kptr_stash_simple_2();

nit: Can you use same name in

if (test__start_subtest("$NAME"))
  $NAME();

so test_local_kptr_stash_simple would
be renamed to local_kptr_stash_simple_yes_special_field
and similar for test_local_kptr_stash_simple_2.

This way 'git grep' for failing subtest name
will quickly find the right prog_tests subtest
runner func.

>  	if (test__start_subtest("local_kptr_stash_unstash"))
>  		test_local_kptr_stash_unstash();
>  	if (test__start_subtest("local_kptr_stash_fail"))
> diff --git a/tools/testing/selftests/bpf/progs/local_kptr_stash.c b/tools/testing/selftests/bpf/progs/local_kptr_stash.c
> index 06838083079c..4de548c31aab 100644
> --- a/tools/testing/selftests/bpf/progs/local_kptr_stash.c
> +++ b/tools/testing/selftests/bpf/progs/local_kptr_stash.c
> @@ -14,10 +14,16 @@ struct node_data {
>  	struct bpf_rb_node node;
>  };
>  
> +struct node_data2 {
> +	long key;
> +	long data;
> +};
> +

Since this has no special fields, it's not a collection node. I've been using
'node_data' and similar naming pattern in selftests for collection nodes
specifically, this muddles the meaning a bit. Can the name be changed to
something else? 'struct plain_local' maybe? I don't feel strongly about
'plain_local', though, anything distinct enough from 'node_data' is fine by me.

>  struct map_value {
>  	struct prog_test_ref_kfunc *not_kptr;
>  	struct prog_test_ref_kfunc __kptr *val;
>  	struct node_data __kptr *node;
> +	struct node_data2 __kptr *node2;

Similar naming nit here. Maybe 'node2' -> 'plain'?

Aside from the naming nits, LGTM.

>  };
>  
>  /* This is necessary so that LLVM generates BTF for node_data struct
> @@ -66,6 +72,28 @@ long stash_rb_nodes(void *ctx)
>  	return create_and_stash(0, 41) ?: create_and_stash(1, 42);
>  }
>  
> +SEC("tc")
> +long stash_rb_nodes_2(void *ctx)
> +{
> +	struct map_value *mapval;
> +	struct node_data2 *res;
> +	int idx = 0;
> +
> +	mapval = bpf_map_lookup_elem(&some_nodes, &idx);
> +	if (!mapval)
> +		return 1;
> +
> +	res = bpf_obj_new(typeof(*res));
> +	if (!res)
> +		return 1;
> +	res->key = 41;
> +
> +	res = bpf_kptr_xchg(&mapval->node2, res);
> +	if (res)
> +		bpf_obj_drop(res);
> +	return 0;
> +}
> +
>  SEC("tc")
>  long unstash_rb_node(void *ctx)
>  {




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