linux-kernel - [patch 15/50] locking/rtmutex: Provide rt_mutex_wake

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Date:   Tue, 13 Jul 2021 17:11:09 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: [patch 15/50] locking/rtmutex: Provide rt_mutex_wake_q and helpers

From: Thomas Gleixner <tglx@...utronix.de>

To handle the difference of wakeups for regular sleeping locks (mutex,
rtmutex, rw_semaphore) and the wakeups for 'sleeping' spin/rwlocks on
PREEMPT_RT enabled kernels correctly, it is required to provide a
wake_q construct which allows to keep them seperate.

Provide a wrapper around wake_q and the required helpers, which will be
extended with the state handling later.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/locking/rtmutex.c        | 15 +++++++++++++++
 kernel/locking/rtmutex_common.h | 14 ++++++++++++++
 2 files changed, 29 insertions(+)
---
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 2aaf3bfc1052..db3103e2733b 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -347,6 +347,21 @@ static __always_inline void rt_mutex_adjust_prio(struct task_struct *p)
 	rt_mutex_setprio(p, pi_task);
 }
 
+/* RT mutex specific wake_q wrappers */
+static __always_inline void rt_mutex_wake_q_add(struct rt_mutex_wake_q_head *wqh,
+						struct rt_mutex_waiter *w)
+{
+	wake_q_add(&wqh->head, w->task);
+}
+
+static __always_inline void rt_mutex_wake_up_q(struct rt_mutex_wake_q_head *wqh)
+{
+	wake_up_q(&wqh->head);
+
+	/* Pairs with preempt_disable() in mark_wakeup_next_waiter() */
+	preempt_enable();
+}
+
 /*
  * Deadlock detection is conditional:
  *
diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index dbd261911fdc..b1ea7fe88546 100644
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -39,6 +39,20 @@ struct rt_mutex_waiter {
 	u64			deadline;
 };
 
+/**
+ * rt_mutex_wake_q_head - Wrapper around regular wake_q_head to support
+ *			  "sleeping" spinlocks on RT
+ * @head:		The regular wake_q_head for sleeping lock variants
+ */
+struct rt_mutex_wake_q_head {
+	struct wake_q_head	head;
+};
+
+#define DEFINE_RT_MUTEX_WAKE_Q_HEAD(name)				\
+	struct rt_mutex_wake_q_head name = {				\
+		.head		= WAKE_Q_HEAD_INITIALIZER(name.head),	\
+	}
+
 /*
  * PI-futex support (proxy locking functions, etc.):
  */