[Draft] selftests/x86/fsgsbase_64 test problem

I don't know if this is worth reporting - please let me know what your thoughts are on the following email. Recipients are from 'get_maintainer.pl -f tools/testing/selftests/x86/fsgsbase.c'.

--- To: Shuah Khan shuah@kernel.org, Ingo Molnar mingo@kernel.org, Andy Lutomirski luto@kernel.org, Dmitry Safonov dsafonov@virtuozzo.com, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: selftests/x86/fsgsbase_64 test problem

We've noticed that fsgsbase_64 can fail periodically with the following error:

[RUN] ARCH_SET_GS(0x0) and clear gs, then schedule to 0x1 Before schedule, set selector to 0x1 other thread: ARCH_SET_GS(0x1) -- sel is 0x0 [FAIL] GS/BASE changed from 0x1/0x0 to 0x0/0x0

This can be reliably reproduced by running fsgsbase_64 in a loop. i.e.

for i in $(seq 1 10000); do ./fsgsbase_64 || break; done

This problem isn't new - I've reproduced it on latest mainline and every release going back to v4.12 (I did not try earlier).

Thanks, Dan