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

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Date:   Sun, 30 Jan 2022 15:46:27 -0600
From:   Clark Williams <clark.williams@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Thomas Gleixner <tglx@...utronix.org>,
        linux-rt-users@...r.kernel.org, williams@...hat.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH PREEMPT_RT 4.19 STABLE] rt:  PREEMPT_RT safety net for backported patches

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>
---
 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
+
 config HAVE_PREEMPT_LAZY
 	bool

@@ -80,6 +84,7 @@ config PREEMPT_RT_FULL
 	depends on IRQ_FORCED_THREADING
 	select PREEMPT_RT_BASE
 	select PREEMPT_RCU
+	select PREEMPT_RT
 	help
 	  All and everything

-- 
2.34.1