On 9/17/20 9:37 PM, Michael Ellerman wrote:
Shuah Khan skhan@linuxfoundation.org writes:
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 2But 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 13The 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
It can wait for v5.10 IMHO, but up to you.
Good to know. I will send this for 5.10-rc1 then.
thanks, -- Shuah