linux-kernel - [PATCH] preempt: Allow CONFIG_DEBUG_PREEMPT for CONFIG_PREEMPT

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Date:   Wed,  7 Jul 2021 20:23:06 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] preempt: Allow CONFIG_DEBUG_PREEMPT for CONFIG_PREEMPT_VOLUNTARY

While recently staring at some preempt_count dumpster fire for a
CONFIG_PREEMPT_VOLUNTARY kernel, I wished I could turn on
CONFIG_DEBUG_PREEMPT on top of CONFIG_DEBUG_ATOMIC_SLEEP to see *where*
preemption had been disabled. It didn't take much to get that, and although
it didn't help my particular case, I think it can still be useful.

Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
 kernel/sched/core.c | 3 +--
 lib/Kconfig.debug   | 2 +-
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0c22cd026440..5673b85fa22d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5109,8 +5109,7 @@ static inline void sched_tick_start(int cpu) { }
 static inline void sched_tick_stop(int cpu) { }
 #endif
 
-#if defined(CONFIG_PREEMPTION) && (defined(CONFIG_DEBUG_PREEMPT) || \
-				defined(CONFIG_TRACE_PREEMPT_TOGGLE))
+#if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_TRACE_PREEMPT_TOGGLE)
 /*
  * If the value passed in is equal to the current preempt count
  * then we just disabled preemption. Start timing the latency.
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 678c13967580..7fdd45eee343 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1204,7 +1204,7 @@ config DEBUG_TIMEKEEPING
 
 config DEBUG_PREEMPT
 	bool "Debug preemptible kernel"
-	depends on DEBUG_KERNEL && PREEMPTION && TRACE_IRQFLAGS_SUPPORT
+	depends on DEBUG_KERNEL && PREEMPT_COUNT && TRACE_IRQFLAGS_SUPPORT
 	default y
 	help
 	  If you say Y here then the kernel will use a debug variant of the
-- 
2.25.1