linux-kernel - Re: [PATCH] tick/common: Align tick period during sched

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Message-ID: <2023061944-uprising-applaud-990a@gregkh>
Date:   Mon, 19 Jun 2023 08:18:10 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Mathias Krause <minipli@...ecurity.net>,
        Luiz Capitulino <luizcap@...zon.com>,
        Sven-Haegar Koch <haegar@...net.de>,
        "Bhatnagar, Rishabh" <risbhat@...zon.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "sashal@...nel.org" <sashal@...nel.org>, abuehaze@...zon.com,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] tick/common: Align tick period during sched_timer setup.

On Thu, Jun 15, 2023 at 11:18:30AM +0200, Sebastian Andrzej Siewior wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> The tick period is aligned very early while the first clock_event_device
> is registered. The system runs in periodic mode and switches later to
> one-shot mode if possible.
> 
> The next wake-up event is programmed based on aligned value
> (tick_next_period) but the delta value, that is used to program the
> clock_event_device, is computed based on ktime_get().
> 
> With the subtracted offset, the devices fires in less than the exacted
> time frame. With a large enough offset the system programs the timer for
> the next wake-up and the remaining time left is too little to make any
> boot progress. The system hangs.
> 
> Move the alignment later to the setup of tick_sched timer. At this point
> the system switches to oneshot mode and a highres clocksource is
> available. It safe to update tick_next_period ktime_get() will now
> return accurate (not jiffies based) time.
> 
> [bigeasy: Patch description + testing].
> 
> Reported-by: Mathias Krause <minipli@...ecurity.net>
> Reported-by: "Bhatnagar, Rishabh" <risbhat@...zon.com>
> Fixes: e9523a0d81899 ("tick/common: Align tick period with the HZ tick.")
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Link: https://lore.kernel.org/5a56290d-806e-b9a5-f37c-f21958b5a8c0@grsecurity.net
> Link: https://lore.kernel.org/12c6f9a3-d087-b824-0d05-0d18c9bc1bf3@amazon.com
> ---
>  kernel/time/tick-common.c | 11 +----------
>  kernel/time/tick-sched.c  | 13 ++++++++++++-
>  2 files changed, 13 insertions(+), 11 deletions(-)

What's the status of this fix, I didn't see it in -rc7, am I looking in
the wrong place?

thanks,

greg k-h