linux-kernel - Re: [s390x vDSO Bug?] clock_gettime(CLOCK_MONOTONIC

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Message-ID: <YFmUrVOyX4q+8Dy9@osiris>
Date:   Tue, 23 Mar 2021 08:11:41 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Li Wang <liwang@...hat.com>
Cc:     Alexander Gordeev <agordeev@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        LTP List <ltp@...ts.linux.it>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-s390@...r.kernel.org, Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [s390x vDSO Bug?] clock_gettime(CLOCK_MONOTONIC_RAW, ...) gets
 abnormal ts value

On Tue, Mar 23, 2021 at 02:21:52PM +0800, Li Wang wrote:
> Hi linux-s390 experts,
> 
> We observed that LTP/clock_gettime04 always FAIL on s390x with
> kernel-v5.12-rc3.
> To simply show the problem, I rewrite the LTP reproducer as a simple C
> below.
> Maybe it's a new bug introduced from the kernel-5.12 series branch?
> 
> PASS:
> ------------
> # uname -r
> 5.11.0-*.s390x
> 
> # grep TIME_NS /boot/config-5.11.0-*.s390x
> no TIME_NS enabled
> 
> ## ./test-timer
> vdso_ts_nsec = 898169901815, vdso_ts.tv_sec = 898, vdso_ts.tv_nsec =
> 169901815
> sys_ts_nsec  = 898169904269, sys_ts.tv_sec  = 898, sys_ts.tv_nsec  =
> 169904269
> ===> PASS
> 
> FAIL:
> ----------
> # uname -r
> 5.12.0-0.rc3.*.s390x
> 
> # grep TIME_NS /boot/config-5.12.0-0.rc3.s390x
> CONFIG_TIME_NS=y
> CONFIG_GENERIC_VDSO_TIME_NS=y
> 
> # ./test-timer
> vdso_ts_nsec = 4484351380985507, vdso_ts.tv_sec = 4484351, vdso_ts.tv_nsec
> = 380985507
> sys_ts_nsec  = 1446923235377, sys_ts.tv_sec  = 1446, sys_ts.tv_nsec  =
> 923235377
> ===> FAIL

Thanks for reporting!

I'll look later today into this. I would nearly bet that I broke it
with commit f8d8977a3d97 ("s390/time: convert tod_clock_base to
union")