locking/rtmutex: Provide rt_mutex_slowlock_locked()

Split the inner workings of rt_mutex_slowlock() out into a separate
function, which can be reused by the upcoming RT lock substitutions,
e.g. for rw_semaphores.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.841971086@linutronix.de

kernel/locking/rtmutex.c

@@ -1106,7 +1106,7 @@ static void __sched remove_waiter(struct rt_mutex_base *lock,
 }
 
 /**
- * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
+ * rt_mutex_slowlock_block() - Perform the wait-wake-try-to-take loop
  * @lock:		 the rt_mutex to take
  * @state:		 the state the task should block in (TASK_INTERRUPTIBLE
  *			 or TASK_UNINTERRUPTIBLE)
@@ -1115,7 +1115,7 @@ static void __sched remove_waiter(struct rt_mutex_base *lock,
  *
  * Must be called with lock->wait_lock held and interrupts disabled
  */
-static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
+static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
 					   unsigned int state,
 					   struct hrtimer_sleeper *timeout,
 					   struct rt_mutex_waiter *waiter)
@@ -1168,20 +1168,72 @@ static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
 	}
 }
 
-/*
+/**
- * Slow path lock function:
+ * __rt_mutex_slowlock - Locking slowpath invoked with lock::wait_lock held
+ * @lock:	The rtmutex to block lock
+ * @state:	The task state for sleeping
+ * @chwalk:	Indicator whether full or partial chainwalk is requested
+ * @waiter:	Initializer waiter for blocking
  */
-static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
+static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
 				       unsigned int state,
-				     struct hrtimer_sleeper *timeout,
+				       enum rtmutex_chainwalk chwalk,
-				     enum rtmutex_chainwalk chwalk)
+				       struct rt_mutex_waiter *waiter)
+{
+	int ret;
+
+	lockdep_assert_held(&lock->wait_lock);
+
+	/* Try to acquire the lock again: */
+	if (try_to_take_rt_mutex(lock, current, NULL))
+		return 0;
+
+	set_current_state(state);
+
+	ret = task_blocks_on_rt_mutex(lock, waiter, current, chwalk);
+
+	if (likely(!ret))
+		ret = rt_mutex_slowlock_block(lock, state, NULL, waiter);
+
+	if (unlikely(ret)) {
+		__set_current_state(TASK_RUNNING);
+		remove_waiter(lock, waiter);
+		rt_mutex_handle_deadlock(ret, chwalk, waiter);
+	}
+
+	/*
+	 * try_to_take_rt_mutex() sets the waiter bit
+	 * unconditionally. We might have to fix that up.
+	 */
+	fixup_rt_mutex_waiters(lock);
+	return ret;
+}
+
+static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
+					     unsigned int state)
 {
 	struct rt_mutex_waiter waiter;
-	unsigned long flags;
+	int ret;
-	int ret = 0;
 
 	rt_mutex_init_waiter(&waiter);
 
+	ret = __rt_mutex_slowlock(lock, state, RT_MUTEX_MIN_CHAINWALK, &waiter);
+
+	debug_rt_mutex_free_waiter(&waiter);
+	return ret;
+}
+
+/*
+ * rt_mutex_slowlock - Locking slowpath invoked when fast path fails
+ * @lock:	The rtmutex to block lock
+ * @state:	The task state for sleeping
+ */
+static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
+				     unsigned int state)
+{
+	unsigned long flags;
+	int ret;
+
 	/*
 	 * Technically we could use raw_spin_[un]lock_irq() here, but this can
 	 * be called in early boot if the cmpxchg() fast path is disabled
@@ -1191,44 +1243,8 @@ static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
 	 * irqsave/restore variants.
 	 */
 	raw_spin_lock_irqsave(&lock->wait_lock, flags);
-
+	ret = __rt_mutex_slowlock_locked(lock, state);
-	/* Try to acquire the lock again: */
-	if (try_to_take_rt_mutex(lock, current, NULL)) {
 	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
-		return 0;
-	}
-
-	set_current_state(state);
-
-	/* Setup the timer, when timeout != NULL */
-	if (unlikely(timeout))
-		hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
-
-	ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
-
-	if (likely(!ret))
-		/* sleep on the mutex */
-		ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
-
-	if (unlikely(ret)) {
-		__set_current_state(TASK_RUNNING);
-		remove_waiter(lock, &waiter);
-		rt_mutex_handle_deadlock(ret, chwalk, &waiter);
-	}
-
-	/*
-	 * try_to_take_rt_mutex() sets the waiter bit
-	 * unconditionally. We might have to fix that up.
-	 */
-	fixup_rt_mutex_waiters(lock);
-
-	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
-
-	/* Remove pending timer: */
-	if (unlikely(timeout))
-		hrtimer_cancel(&timeout->timer);
-
-	debug_rt_mutex_free_waiter(&waiter);
 
 	return ret;
 }
@@ -1239,7 +1255,7 @@ static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,
 	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
 		return 0;
 
-	return rt_mutex_slowlock(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
+	return rt_mutex_slowlock(lock, state);
 }
 
 static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock)

kernel/locking/rtmutex_api.c

@@ -342,7 +342,7 @@ int __sched rt_mutex_wait_proxy_lock(struct rt_mutex_base *lock,
 	raw_spin_lock_irq(&lock->wait_lock);
 	/* sleep on the mutex */
 	set_current_state(TASK_INTERRUPTIBLE);
-	ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
+	ret = rt_mutex_slowlock_block(lock, TASK_INTERRUPTIBLE, to, waiter);
 	/*
 	 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
 	 * have to fix that up.