linux-kernel - [PATCH 2/3] preempt/dynamic: Introduce preempt mode accessors

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Message-Id: <20220314133738.269522-3-frederic@kernel.org>
Date:   Mon, 14 Mar 2022 14:37:37 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Paul E . McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Marco Elver <elver@...gle.com>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Uladzislau Rezki <uladzislau.rezki@...y.com>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: [PATCH 2/3] preempt/dynamic: Introduce preempt mode accessors

From: Valentin Schneider <valentin.schneider@....com>

CONFIG_PREEMPT{_NONE, _VOLUNTARY} designate either:
o The build-time preemption model when !PREEMPT_DYNAMIC
o The default boot-time preemption model when PREEMPT_DYNAMIC

IOW, using those on PREEMPT_DYNAMIC kernels is meaningless - the actual
model could have been set to something else by the "preempt=foo" cmdline
parameter.

Introduce a set of helpers to determine the actual preemption mode used by
the live kernel.

Suggested-by: Marco Elver <elver@...gle.com>
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Uladzislau Rezki <uladzislau.rezki@...y.com>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Neeraj Upadhyay <quic_neeraju@...cinc.com>
---
 include/linux/sched.h | 16 ++++++++++++++++
 kernel/sched/core.c   | 11 +++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 508b91d57470..d348e886e4d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2096,6 +2096,22 @@ static inline void cond_resched_rcu(void)
 #endif
 }
 
+#ifdef CONFIG_PREEMPT_DYNAMIC
+
+extern bool preempt_mode_none(void);
+extern bool preempt_mode_voluntary(void);
+extern bool preempt_mode_full(void);
+
+#else
+
+#define preempt_mode_none() IS_ENABLED(CONFIG_PREEMPT_NONE)
+#define preempt_mode_voluntary() IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY)
+#define preempt_mode_full() IS_ENABLED(CONFIG_PREEMPT)
+
+#endif
+
+#define preempt_mode_rt() IS_ENABLED(CONFIG_PREEMPT_RT)
+
 /*
  * Does a critical section need to be broken due to another
  * task waiting?: (technically does not depend on CONFIG_PREEMPTION,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2e4ae00e52d1..6e5c8f0f874a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6684,6 +6684,17 @@ static void __init preempt_dynamic_init(void)
 	}
 }
 
+#define PREEMPT_MODE_ACCESSOR(mode) \
+	bool preempt_mode_##mode(void)						 \
+	{									 \
+		WARN_ON_ONCE(preempt_dynamic_mode == preempt_dynamic_undefined); \
+		return preempt_dynamic_mode == preempt_dynamic_##mode;		 \
+	}
+
+PREEMPT_MODE_ACCESSOR(none)
+PREEMPT_MODE_ACCESSOR(voluntary)
+PREEMPT_MODE_ACCESSOR(full)
+
 #else /* !CONFIG_PREEMPT_DYNAMIC */
 
 static inline void preempt_dynamic_init(void) { }
-- 
2.25.1