linux-kernel - Re: [PATCH v3 20/36] s390/time: Set up vDSO datapage later

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Message-ID: <20250917151259.29680Ba8-hca@linux.ibm.com>
Date: Wed, 17 Sep 2025 17:12:59 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Arnd Bergmann <arnd@...db.de>, "David S. Miller" <davem@...emloft.net>,
        Andreas Larsson <andreas@...sler.com>,
        Nick Alcock <nick.alcock@...cle.com>, John Stultz <jstultz@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Shuah Khan <shuah@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, "Theodore Ts'o" <tytso@....edu>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Russell King <linux@...linux.org.uk>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Nagarathnam Muthusamy <nagarathnam.muthusamy@...cle.com>,
        Shannon Nelson <sln@...main.com>, linux-kernel@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
        loongarch@...ts.linux.dev, linux-mips@...r.kernel.org,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH v3 20/36] s390/time: Set up vDSO datapage later

On Wed, Sep 17, 2025 at 04:00:22PM +0200, Thomas Weißschuh wrote:
> Upcoming changes to the generic vDSO library will mean that the vDSO
> datapage will not yet be usable during time_early_init().
> 
> Move the initialization to time_init() which is called later. This is
> valid as the value of tod_clock_base.tod does not change during the
> lifetime of the machine and the vDSO datapage is only used much later.

This is not true; tod_clock_base is a union and the tod member is changed
implicitly within clock_sync_global():

	tod_clock_base.eitod += delta;

However that happens only in stop_machine() context. Therefore moving the
initialization to time_init() is indeed ok, since it is called very early
when even preemption is still disabled.

I would appreciate if you would change the commit message a bit.

In any case:
Acked-by: Heiko Carstens <hca@...ux.ibm.com>