Messages in this thread | | | Subject | Re: [PATCH] selftests/harness: Flush stdout before forking | From | Shuah Khan <> | Date | Thu, 17 Sep 2020 06:58:23 -0600 |
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On 9/16/20 10:53 PM, Max Filippov wrote: > On Wed, Sep 16, 2020 at 9:16 PM Michael Ellerman <mpe@ellerman.id.au> 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@ellerman.id.au> >> --- >> tools/testing/selftests/kselftest_harness.h | 5 +++++ >> 1 file changed, 5 insertions(+) > > Tested-by: Max Filippov <jcmvbkbc@gmail.com> >
Thank you both. Applying to linux-kselftest fixes for 5.9-rc7
thanks, -- Shuah
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