[patch 12/14] locking/rtmutex: Consolidate the fast/slowpath invocation

Thomas Gleixner
2021-03-23T21:41:54Z

The indirection via a function pointer (which is at least optimized into a
tail call by the compiler) is making the code hard to read.

Clean it up and move the futex related trylock functions down to the futex
section.

Move the wake_q wakeup into rt_mutex_slowunlock(). No point in handing it
to the caller. The futex code uses a different function.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/locking/rtmutex.c | 129 +++++++++++++++++------------------------------
1 file changed, 49 insertions(+), 80 deletions(-)

--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1299,13 +1299,24 @@ static int __sched rt_mutex_slowtrylock(
}

/*
+ * Performs the wakeup of the top-waiter and re-enables preemption.
+ */
+void __sched rt_mutex_postunlock(struct wake_q_head *wake_q)
+{
+ wake_up_q(wake_q);
+
+ /* Pairs with preempt_disable() in rt_mutex_slowunlock() */
+ preempt_enable();
+}
+
+/*
* Slow path to release a rt-mutex.
*
* Return whether the current task needs to call rt_mutex_postunlock().
*/
-static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
- struct wake_q_head *wake_q)
+static void __sched rt_mutex_slowunlock(struct rt_mutex *lock)
{
+ DEFINE_WAKE_Q(wake_q);
unsigned long flags;

/* irqsave required to support early boot calls */
@@ -1347,7 +1358,7 @@ static bool __sched rt_mutex_slowunlock(
while (!rt_mutex_has_waiters(lock)) {
/* Drops lock->wait_lock ! */
if (unlock_rt_mutex_safe(lock, flags) == true)
- return false;
+ return;
/* Relock the rtmutex and try again */
raw_spin_lock_irqsave(&lock->wait_lock, flags);
}
@@ -1358,10 +1369,10 @@ static bool __sched rt_mutex_slowunlock(
*
* Queue the next waiter for wakeup once we release the wait_lock.
*/
- mark_wakeup_next_waiter(wake_q, lock);
+ mark_wakeup_next_waiter(&wake_q, lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

- return true; /* call rt_mutex_postunlock() */
+ rt_mutex_postunlock(&wake_q);
}

/*
@@ -1370,60 +1381,20 @@ static bool __sched rt_mutex_slowunlock(
* The atomic acquire/release ops are compiled away, when either the
* architecture does not support cmpxchg or when debugging is enabled.
*/
-static __always_inline int
-rt_mutex_fastlock(struct rt_mutex *lock, int state,
- int (*slowfn)(struct rt_mutex *lock, int state,
- struct hrtimer_sleeper *timeout,
- enum rtmutex_chainwalk chwalk))
+static __always_inline int __rt_mutex_lock(struct rt_mutex *lock, long state)
{
- if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
- return 0;
+ int ret;

- return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
-}
+ might_sleep();

-static __always_inline int
-rt_mutex_fasttrylock(struct rt_mutex *lock,
- int (*slowfn)(struct rt_mutex *lock))
-{
if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
- return 1;
-
- return slowfn(lock);
-}
-
-/*
- * Performs the wakeup of the top-waiter and re-enables preemption.
- */
-void __sched rt_mutex_postunlock(struct wake_q_head *wake_q)
-{
- wake_up_q(wake_q);
-
- /* Pairs with preempt_disable() in rt_mutex_slowunlock() */
- preempt_enable();
-}
-
-static __always_inline void
-rt_mutex_fastunlock(struct rt_mutex *lock,
- bool (*slowfn)(struct rt_mutex *lock,
- struct wake_q_head *wqh))
-{
- DEFINE_WAKE_Q(wake_q);
-
- if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
- return;
-
- if (slowfn(lock, &wake_q))
- rt_mutex_postunlock(&wake_q);
-}
+ return 0;

-static __always_inline void __rt_mutex_lock(struct rt_mutex *lock,
- unsigned int subclass)
-{
- might_sleep();
+ ret = rt_mutex_slowlock(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
+ if (ret)
+ mutex_release(&lock->dep_map, _RET_IP_);

- mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
- rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
+ return ret;
}

#ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -1435,7 +1406,8 @@ static __always_inline void __rt_mutex_l
*/
void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
{
- __rt_mutex_lock(lock, subclass);
+ mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
+ __rt_mutex_lock(lock);
}
EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);

@@ -1448,7 +1420,7 @@ EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
*/
void __sched rt_mutex_lock(struct rt_mutex *lock)
{
- __rt_mutex_lock(lock, 0);
+ __rt_mutex_lock(lock, TASK_UNINTERRUPTIBLE);
}
EXPORT_SYMBOL_GPL(rt_mutex_lock);
#endif
@@ -1464,32 +1436,10 @@ EXPORT_SYMBOL_GPL(rt_mutex_lock);
*/
int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
{
- int ret;
-
- might_sleep();
-
- mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
- ret = rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
- if (ret)
- mutex_release(&lock->dep_map, _RET_IP_);
-
- return ret;
+ return __rt_mutex_lock(lock, TASK_INTERRUPTIBLE);
}
EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);

-/*
- * Futex variant, must not use fastpath.
- */
-int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
-{
- return rt_mutex_slowtrylock(lock);
-}
-
-int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
-{
- return __rt_mutex_slowtrylock(lock);
-}
-
/**
* rt_mutex_trylock - try to lock a rt_mutex
*
@@ -1508,7 +1458,10 @@ int __sched rt_mutex_trylock(struct rt_m
if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
return 0;

- ret = rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
+ if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
+ return 1;
+
+ ret = rt_mutex_slowtrylock(lock);
if (ret)
mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);

@@ -1524,10 +1477,26 @@ EXPORT_SYMBOL_GPL(rt_mutex_trylock);
void __sched rt_mutex_unlock(struct rt_mutex *lock)
{
mutex_release(&lock->dep_map, _RET_IP_);
- rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
+ if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
+ return;
+
+ rt_mutex_slowunlock(lock);
}
EXPORT_SYMBOL_GPL(rt_mutex_unlock);

+/*
+ * Futex variants, must not use fastpath.
+ */
+int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
+{
+ return rt_mutex_slowtrylock(lock);
+}
+
+int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
+{
+ return __rt_mutex_slowtrylock(lock);
+}
+
/**
* __rt_mutex_futex_unlock - Futex variant, that since futex variants
* do not use the fast-path, can be simple and will not need to retry.