linux-kernel - [patch V3 30/64] locking/rtmutex: Provide the spin/rwlock core lock function

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Date:   Thu, 05 Aug 2021 17:13:30 +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>,
        Mike Galbraith <efault@....de>
Subject: [patch V3 30/64] locking/rtmutex: Provide the spin/rwlock core lock function

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

A simplified version of the rtmutex slowlock function which neither handles
signals nor timeouts and is careful about preserving the state of the
blocked task across the lock operation.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/locking/rtmutex.c        |   60 ++++++++++++++++++++++++++++++++++++++++
 kernel/locking/rtmutex_common.h |    2 -
 2 files changed, 61 insertions(+), 1 deletion(-)
---
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1416,3 +1416,63 @@ static __always_inline int __rt_mutex_lo
 	return rt_mutex_slowlock(lock, state);
 }
 #endif /* RT_MUTEX_BUILD_MUTEX */
+
+#ifdef RT_MUTEX_BUILD_SPINLOCKS
+/*
+ * Functions required for spin/rw_lock substitution on RT kernels
+ */
+
+/**
+ * rtlock_slowlock_locked - Slow path lock acquisition for RT locks
+ * @lock:	The underlying rt mutex
+ */
+static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
+{
+	struct rt_mutex_waiter waiter;
+
+	lockdep_assert_held(&lock->wait_lock);
+
+	if (try_to_take_rt_mutex(lock, current, NULL))
+		return;
+
+	rt_mutex_init_rtlock_waiter(&waiter);
+
+	/* Save current state and set state to TASK_RTLOCK_WAIT */
+	current_save_and_set_rtlock_wait_state();
+
+	task_blocks_on_rt_mutex(lock, &waiter, current, RT_MUTEX_MIN_CHAINWALK);
+
+	for (;;) {
+		/* Try to acquire the lock again. */
+		if (try_to_take_rt_mutex(lock, current, &waiter))
+			break;
+
+		raw_spin_unlock_irq(&lock->wait_lock);
+
+		schedule_rtlock();
+
+		raw_spin_lock_irq(&lock->wait_lock);
+		set_current_state(TASK_RTLOCK_WAIT);
+	}
+
+	/* Restore the task state */
+	current_restore_rtlock_saved_state();
+
+	/*
+	 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We
+	 * might have to fix that up:
+	 */
+	fixup_rt_mutex_waiters(lock);
+	debug_rt_mutex_free_waiter(&waiter);
+}
+
+static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&lock->wait_lock, flags);
+	rtlock_slowlock_locked(lock);
+	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+}
+
+#endif /* RT_MUTEX_BUILD_SPINLOCKS */
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -181,7 +181,7 @@ static inline void rt_mutex_init_waiter(
 	waiter->task = NULL;
 }
 
-static inline void rtlock_init_rtmutex_waiter(struct rt_mutex_waiter *waiter)
+static inline void rt_mutex_init_rtlock_waiter(struct rt_mutex_waiter *waiter)
 {
 	rt_mutex_init_waiter(waiter);
 	waiter->wake_state = TASK_RTLOCK_WAIT;