Re: [PATCH] selftests/harness: Flush stdout before forking

On Thu, Sep 17, 2020 at 02:15:19PM +1000, Michael Ellerman 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

Oh thank you for tracking this down! I thought seccomp wasn't killing a child or something, and hadn't found it yet. :)

Acked-by: Kees Cook keescook@chromium.org