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selftests/bpf: Fix htab_update/reenter_update selftest failure #10303

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selftests/bpf: Fix htab_update/reenter_update selftest failure #10303

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37 changes: 28 additions & 9 deletions tools/testing/selftests/bpf/prog_tests/htab_update.c
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Original file line number Diff line number Diff line change
Expand Up @@ -15,32 +15,51 @@ struct htab_update_ctx {
static void test_reenter_update(void)
{
struct htab_update *skel;
unsigned int key, value;
void *value = NULL;
unsigned int key, value_size;
int err;

skel = htab_update__open();
if (!ASSERT_OK_PTR(skel, "htab_update__open"))
return;

/* lookup_elem_raw() may be inlined and find_kernel_btf_id() will return -ESRCH */
bpf_program__set_autoload(skel->progs.lookup_elem_raw, true);
bpf_program__set_autoload(skel->progs.bpf_obj_free_fields, true);
err = htab_update__load(skel);
if (!ASSERT_TRUE(!err || err == -ESRCH, "htab_update__load") || err)
if (!ASSERT_TRUE(!err, "htab_update__load") || err)
goto out;

skel->bss->pid = getpid();
err = htab_update__attach(skel);
if (!ASSERT_OK(err, "htab_update__attach"))
goto out;

/* Will trigger the reentrancy of bpf_map_update_elem() */
value_size = bpf_map__value_size(skel->maps.htab);

value = calloc(1, value_size);
if (!ASSERT_OK_PTR(value, "calloc value"))
goto out;
/*
* First update: plain insert. This should NOT trigger the re-entrancy
* path, because there is no old element to free yet.
*/
key = 0;
value = 0;
err = bpf_map_update_elem(bpf_map__fd(skel->maps.htab), &key, &value, 0);
if (!ASSERT_OK(err, "add element"))
err = bpf_map_update_elem(bpf_map__fd(skel->maps.htab), &key, value, BPF_ANY);
if (!ASSERT_OK(err, "first update (insert)"))
goto out;

/*
* Second update: replace existing element with same key and trigger
* the reentrancy of bpf_map_update_elem().
* check_and_free_fields() calls bpf_obj_free_fields() on the old
* value, which is where fentry program runs and performs a nested
* bpf_map_update_elem(), triggering -EDEADLK.
*/
memset(value, 0, value_size);
err = bpf_map_update_elem(bpf_map__fd(skel->maps.htab), &key, value, BPF_ANY);
if (!ASSERT_OK(err, "second update (replace)"))
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);
}
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19 changes: 13 additions & 6 deletions tools/testing/selftests/bpf/progs/htab_update.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6,24 +6,31 @@

char _license[] SEC("license") = "GPL";

/* Map value type: has BTF-managed field (bpf_timer) */
struct val {
struct bpf_timer t;
__u64 payload;
};

struct {
__uint(type, BPF_MAP_TYPE_HASH);
__uint(max_entries, 1);
__uint(key_size, sizeof(__u32));
__uint(value_size, sizeof(__u32));
__type(key, __u32);
__type(value, struct val);
} htab SEC(".maps");

int pid = 0;
int update_err = 0;

SEC("?fentry/lookup_elem_raw")
int lookup_elem_raw(void *ctx)
SEC("?fentry/bpf_obj_free_fields")
int bpf_obj_free_fields(void *ctx)
{
__u32 key = 0, value = 1;
__u32 key = 0;
struct val value = { .payload = 1 };

if ((bpf_get_current_pid_tgid() >> 32) != pid)
return 0;

update_err = bpf_map_update_elem(&htab, &key, &value, 0);
update_err = bpf_map_update_elem(&htab, &key, &value, BPF_ANY);
return 0;
}
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