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selftests/bpf: Remove flaky test_btf_id test

With previous patch, one of subtests in test_btf_id becomes
flaky and may fail. The following is a failing example:

Error: #26 btf
Error: #26/174 btf/BTF ID
Error: #26/174 btf/BTF ID
btf_raw_create:PASS:check 0 nsec
btf_raw_create:PASS:check 0 nsec
test_btf_id:PASS:check 0 nsec
...
test_btf_id:PASS:check 0 nsec
test_btf_id:FAIL:check BTF lingersdo_test_get_info:FAIL:check failed: -1

The test tries to prove a btf_id not available after the map is closed.
But btf_id is freed only after workqueue and a rcu grace period, compared
to previous case just after a rcu grade period.
Depending on system workload, workqueue could take quite some time
to execute function bpf_map_free_deferred() which may cause the test failure.
Instead of adding arbitrary delays, let us remove the logic to
check btf_id availability after map is closed.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20231214203820.1469402-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

authored by

Yonghong Song and committed by
Alexei Starovoitov 56925f38 59e5791f

-5
-5
tools/testing/selftests/bpf/prog_tests/btf.c
··· 4630 4630 /* The map holds the last ref to BTF and its btf_id */ 4631 4631 close(map_fd); 4632 4632 map_fd = -1; 4633 - btf_fd[0] = bpf_btf_get_fd_by_id(map_info.btf_id); 4634 - if (CHECK(btf_fd[0] >= 0, "BTF lingers")) { 4635 - err = -1; 4636 - goto done; 4637 - } 4638 4633 4639 4634 fprintf(stderr, "OK"); 4640 4635