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From: Ankur Arora <ankur.a.arora@oracle.com>
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Cc: tglx@linutronix.de, peterz@infradead.org, torvalds@linux-foundation.org,
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        sshegde@linux.ibm.com, boris.ostrovsky@oracle.com,
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Subject: [PATCH v2 14/35] rcu: limit PREEMPT_RCU to full preemption under PREEMPT_AUTO
Date: Mon, 27 May 2024 17:35:00 -0700
Message-Id: <20240528003521.979836-15-ankur.a.arora@oracle.com>
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Under PREEMPT_AUTO, CONFIG_PREEMPTION is enabled, and much like
PREEMPT_DYNAMIC, PREEMPT_AUTO also allows for dynamic switching
of preemption models.

The RCU model, however, is fixed at compile time.

Now, RCU typically selects PREEMPT_RCU if CONFIG_PREEMPTION is enabled.
Given the trade-offs between PREEMPT_RCU=y and PREEMPT_RCU=n, some
configurations might prefer the stronger forward-progress guarantees
of PREEMPT_RCU=n.

Accordingly, select PREEMPT_RCU=y only if the user selects
CONFIG_PREEMPT at compile time.

Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 kernel/rcu/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index e7d2dd267593..9dedb70ac2e6 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -18,7 +18,7 @@ config TREE_RCU
 
 config PREEMPT_RCU
 	bool
-	default y if PREEMPTION
+	default y if (PREEMPT || PREEMPT_DYNAMIC || PREEMPT_RT)
 	select TREE_RCU
 	help
 	  This option selects the RCU implementation that is
-- 
2.31.1