linux-kernel - Re: [PATCH 12/14] vdso/gettimeofday: Add support for auxiliary clocks

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Message-ID: <CANDhNCqvKOc9JgphQwr0eDyJiyG4oLFS9R8rSFvU0fpurrJFDg@mail.gmail.com>
Date: Wed, 20 Aug 2025 01:03:56 -0700
From: John Stultz <jstultz@...gle.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Vincenzo Frascino <vincenzo.frascino@....com>, Shuah Khan <shuah@...nel.org>, 
	Anna-Maria Behnsen <anna-maria@...utronix.de>, Frederic Weisbecker <frederic@...nel.org>, 
	Stephen Boyd <sboyd@...nel.org>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-arch@...r.kernel.org, Richard Cochran <richardcochran@...il.com>, 
	Christopher Hall <christopher.s.hall@...el.com>, Miroslav Lichvar <mlichvar@...hat.com>, 
	Werner Abt <werner.abt@...nberg-usa.com>, David Woodhouse <dwmw2@...radead.org>, 
	Kurt Kanzenbach <kurt@...utronix.de>, Nam Cao <namcao@...utronix.de>, 
	Antoine Tenart <atenart@...nel.org>
Subject: Re: [PATCH 12/14] vdso/gettimeofday: Add support for auxiliary clocks

On Tue, Jul 1, 2025 at 1:58 AM Thomas Weißschuh
<thomas.weissschuh@...utronix.de> wrote:
>
> Expose the auxiliary clocks through the vDSO.
>
> Architectures not using the generic vDSO time framework,
> namely SPARC64, are not supported.
>
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>

Just as a heads up, I've just been bisecting and this commit seems to
be causing problems on arm64 devices, running 32bit versions of
kselftest nanosleep or inconsistency-check tests. Running the 64bit
versions of the tests are not showing issues.

>From my initial digging, it looks like clockids that aren't vdso
enabled (CLOCK_PROCESS_CPUTIME_ID, CLOCK_THREAD_CPUTIME_ID,
CLOCK_REALTIME_ALARM, CLOCK_BOOTTIME_ALARM) are somehow getting caught
in the vdso logic and are *not* falling back to the syscall (stracing
the test I don't see syscalls happen before the failure), and the
values returned don't look to be correct.

The inconsistency-check output looks like:
# 5983032:0
# 5983317:0
# 5983561:0
# 5983846:0
# 5984130:0
# 5984415:0
# --------------------
# 5984659:0
# 2009440:0
# --------------------
# 2009724:0
# 2009969:0
# 2010253:0
# 2010538:0
# 2010782:0
# 2011067:0

Which hints we're returning nanosecond values in the tv_sec field somehow.

Reverting just this change gets things back to working.

It's pretty late here, so I'm going to try to dig a bit further to
understand what's going on tomorrow, but wanted to raise this in case
it's more obvious to less tired eyes. :)

thanks
-john