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[ Upstream commitae24fc8a16] Currently, test_perf_branches_no_hw() relies on the busy loop within test_perf_branches_common() being slow enough to allow at least one perf event sample tick to occur before starting to tear down the backing perf event BPF program. With a relatively small fixed iteration count of 1,000,000, this is not guaranteed on modern fast CPUs, resulting in the test run to subsequently fail with the following: bpf_testmod.ko is already unloaded. Loading bpf_testmod.ko... Successfully loaded bpf_testmod.ko. test_perf_branches_common:PASS:test_perf_branches_load 0 nsec test_perf_branches_common:PASS:attach_perf_event 0 nsec test_perf_branches_common:PASS:set_affinity 0 nsec check_good_sample:PASS:output not valid 0 nsec check_good_sample:PASS:read_branches_size 0 nsec check_good_sample:PASS:read_branches_stack 0 nsec check_good_sample:PASS:read_branches_stack 0 nsec check_good_sample:PASS:read_branches_global 0 nsec check_good_sample:PASS:read_branches_global 0 nsec check_good_sample:PASS:read_branches_size 0 nsec test_perf_branches_no_hw:PASS:perf_event_open 0 nsec test_perf_branches_common:PASS:test_perf_branches_load 0 nsec test_perf_branches_common:PASS:attach_perf_event 0 nsec test_perf_branches_common:PASS:set_affinity 0 nsec check_bad_sample:FAIL:output not valid no valid sample from prog Summary: 0/1 PASSED, 0 SKIPPED, 1 FAILED Successfully unloaded bpf_testmod.ko. On a modern CPU (i.e. one with a 3.5 GHz clock rate), executing 1 million increments of a volatile integer can take significantly less than 1 millisecond. If the spin loop and detachment of the perf event BPF program elapses before the first 1 ms sampling interval elapses, the perf event will never end up firing. Fix this by bumping the loop iteration counter a little within test_perf_branches_common(), along with ensuring adding another loop termination condition which is directly influenced by the backing perf event BPF program executing. Notably, a concious decision was made to not adjust the sample_freq value as that is just not a reliable way to go about fixing the problem. It effectively still leaves the race window open. Fixes:67306f84ca("selftests/bpf: Add bpf_read_branch_records() selftest") Signed-off-by: Matt Bobrowski <mattbobrowski@google.com> Reviewed-by: Jiri Olsa <jolsa@kernel.org> Link: https://lore.kernel.org/r/20251119143540.2911424-1-mattbobrowski@google.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>