linux-kernel - Re: [PATCH PREEMPT_RT 4.19 STABLE] rt: PREEMPT

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Message-ID: <Yfe4uHYEC+syPy/J@linutronix.de>
Date:   Mon, 31 Jan 2022 11:23:52 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Clark Williams <clark.williams@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.org>,
        linux-rt-users@...r.kernel.org, williams@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH PREEMPT_RT 4.19 STABLE] rt:  PREEMPT_RT safety net for
 backported patches

On 2022-01-30 15:46:27 [-0600], Clark Williams wrote:
> While doing some 4.19-rt cleanup work, I stumbled across the fact that parts of
> two backported patches were dependent on CONFIG_PREEMPT_RT, rather than
> the CONFIG_PREEMPT_RT_FULL used in 4.19 and earlier RT series.  The commits
> in the linux-stable-rt v4.19-rt branch are:
> 
> dad4c6a33bf4e mm: slub: Don't resize the location tracking cache on PREEMPT_RT
> e626b6f873f2c net: Treat __napi_schedule_irqoff() as __napi_schedule() on PREEMPT_RT
> 
> Discussing this at the Stable RT maintainers meeting, Steven Rostedt suggested that
> we automagically select CONFIG_PREEMPT_RT if CONFIG_PREEMPT_RT_FULL is on, giving
> us a safety net for any subsequently backported patches. Here's my first cut at
> that patch.
> 
> I suspect we'll need a similar patch for stable RT kernels < 4.19.
> 
> Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Clark Williams <williams@...hat.com>
Acked-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

> ---
>  kernel/Kconfig.preempt | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
> index 306567f72a3e..951f58cbd652 100644
> --- a/kernel/Kconfig.preempt
> +++ b/kernel/Kconfig.preempt
> @@ -6,6 +6,10 @@ config PREEMPT_RT_BASE
>  	bool
>  	select PREEMPT
>  
> +config PREEMPT_RT
> +       bool
> +       default false

default is false.

> +
>  config HAVE_PREEMPT_LAZY
>  	bool
>  

Sebastian