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From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     linux-kernel@vger.kernel.org
Cc:     Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        John Stultz <jstultz@google.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Mel Gorman <mgorman@suse.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Valentin Schneider <vschneid@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [RFC PATCH 1/3] sched/core: Provide a method to check if a task is PI-boosted.
Date:   Fri,  4 Aug 2023 13:30:37 +0200
Message-Id: <20230804113039.419794-2-bigeasy@linutronix.de>
In-Reply-To: <20230804113039.419794-1-bigeasy@linutronix.de>
References: <20230804113039.419794-1-bigeasy@linutronix.de>
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Provide a method to check if a task inherited the priority from another
task. This happens if a task owns a lock which is requested by a task
with higher priority. This can be used as a hint to add a preemption
point to the critical section.

Provide a function which reports true if the task is PI-boosted.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/sched.h |  1 +
 kernel/sched/core.c   | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 609bde814cb06..77fd274133750 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1887,6 +1887,7 @@ static inline int dl_task_check_affinity(struct task_=
struct *p, const struct cpu
 }
 #endif
=20
+extern bool task_is_pi_boosted(const struct task_struct *p);
 extern int yield_to(struct task_struct *p, bool preempt);
 extern void set_user_nice(struct task_struct *p, long nice);
 extern int task_prio(const struct task_struct *p);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c52c2eba7c739..132f06522efa0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8886,6 +8886,21 @@ static inline void preempt_dynamic_init(void) { }
=20
 #endif /* #ifdef CONFIG_PREEMPT_DYNAMIC */
=20
+/*
+ * task_is_pi_boosted - Check if task has been PI boosted.
+ * @p:	Task to check.
+ *
+ * Return true if task is subject to priority inheritance.
+ */
+bool task_is_pi_boosted(const struct task_struct *p)
+{
+	int prio =3D p->prio;
+
+	if (!rt_prio(prio))
+		return false;
+	return prio !=3D p->normal_prio;
+}
+
 /**
  * yield - yield the current processor to other threads.
  *
--=20
2.40.1