linux-kernel - Re: [PATCH v2 23/25] timekeeping: Rework do_adjtimex() to use shadow

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Message-ID: <CANDhNCoQO_EWXGoxJfk2k1qp1uq+eftEb1wtcg6yQZ9d+CAcDw@mail.gmail.com>
Date: Thu, 24 Oct 2024 15:26:06 -0700
From: John Stultz <jstultz@...gle.com>
To: Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc: Frederic Weisbecker <frederic@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	Miroslav Lichvar <mlichvar@...hat.com>, Richard Cochran <richardcochran@...il.com>, 
	Christopher S Hall <christopher.s.hall@...el.com>
Subject: Re: [PATCH v2 23/25] timekeeping: Rework do_adjtimex() to use shadow_timekeeper

On Wed, Oct 9, 2024 at 1:29 AM Anna-Maria Behnsen
<anna-maria@...utronix.de> wrote:
>
> From: Anna-Maria Behnsen <anna-maria@...utronix.de>
>
> Updates of the timekeeper can be done by operating on the shadow timekeeper
> and afterwards copying the result into the real timekeeper. This has the
> advantage, that the sequence count write protected region is kept as small
> as possible.
>
> Convert do_adjtimex() to use this scheme and take the opportunity to use a
> scoped_guard() for locking.
>
> That requires to have a separate function for updating the leap state so
> that the update is protected by the sequence count. This also brings the
> timekeeper and the shadow timekeeper in sync for this state, which was not
> the case so far. That's not a correctness problem as the state is only used
> at the read sides which use the real timekeeper, but it's inconsistent
> nevertheless.
>
> Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>

Again, the tk_shadow naming nit, but otherwise:
Acked-by: John Stultz <jstultz@...gle.com>