Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 26 Jan 2018 09:36:31 -0600
From:   Dan Rue <dan.rue@linaro.org>
To:     Shuah Khan <shuah@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Dmitry Safonov <dsafonov@virtuozzo.com>,
        Borislav Petkov <bp@alien8.de>,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: selftests/x86/fsgsbase_64 test problem
Message-ID: <20180126153631.ha7yc33fj5uhitjo@xps>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: NeoMutt/20171215
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

We've noticed that fsgsbase_64 can fail intermittently 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). This was tested on
a Supermicro board with a Xeon E3-1220 as well as an Intel Nuc with an
i3-5010U.

Thanks,
Dan