Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx> writes: > On 9/16/20 10:53 PM, Max Filippov wrote: >> On Wed, Sep 16, 2020 at 9:16 PM Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote: >>> >>> The test harness forks() a child to run each test. Both the parent and >>> the child print to stdout using libc functions. That can lead to >>> duplicated (or more) output if the libc buffers are not flushed before >>> forking. >>> >>> It's generally not seen when running programs directly, because stdout >>> will usually be line buffered when it's pointing to a terminal. >>> >>> This was noticed when running the seccomp_bpf test, eg: >>> >>> $ ./seccomp_bpf | tee test.log >>> $ grep -c "TAP version 13" test.log >>> 2 >>> >>> But we only expect the TAP header to appear once. >>> >>> It can be exacerbated using stdbuf to increase the buffer size: >>> >>> $ stdbuf -o 1MB ./seccomp_bpf > test.log >>> $ grep -c "TAP version 13" test.log >>> 13 >>> >>> The fix is simple, we just flush stdout & stderr before fork. Usually >>> stderr is unbuffered, but that can be changed, so flush it as well >>> just to be safe. >>> >>> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> >>> --- >>> tools/testing/selftests/kselftest_harness.h | 5 +++++ >>> 1 file changed, 5 insertions(+) >> >> Tested-by: Max Filippov <jcmvbkbc@xxxxxxxxx> > > Thank you both. Applying to linux-kselftest fixes for 5.9-rc7 It can wait for v5.10 IMHO, but up to you. cheers
