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Message-Id: <20210326153944.247927548@linutronix.de>
Date: Fri, 26 Mar 2021 16:29:41 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
Steven Rostedt <rostedt@...dmis.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [patch V2 12/15] locking/rtmutex: Consolidate the fast/slowpath invocation
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@...utronix.de>
---
V2: Make lockdep work by design and not just by chance
---
kernel/locking/rtmutex.c | 144 +++++++++++++++++++----------------------------
1 file changed, 59 insertions(+), 85 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 +1381,21 @@ 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,
+ unsigned int subclass)
{
- if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
- return 0;
+ int ret;
- return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
-}
+ might_sleep();
+ mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
-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);
-}
-
-static __always_inline void __rt_mutex_lock(struct rt_mutex *lock,
- unsigned int subclass)
-{
- might_sleep();
+ return 0;
- mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
- rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
+ ret = rt_mutex_slowlock(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
+ if (ret)
+ mutex_release(&lock->dep_map, _RET_IP_);
+ return ret;
}
#ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -1435,7 +1407,7 @@ 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);
+ __rt_mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass);
}
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, 0);
}
EXPORT_SYMBOL_GPL(rt_mutex_lock);
#endif
@@ -1464,42 +1436,21 @@ 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, 0);
}
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
*
* @lock: the rt_mutex to be locked
*
- * This function can only be called in thread context. It's safe to
- * call it from atomic regions, but not from hard interrupt or soft
- * interrupt context.
+ * This function can only be called in thread context. It's safe to call it
+ * from atomic regions, but not from hard or soft interrupt context.
*
- * Returns 1 on success and 0 on contention
+ * Returns:
+ * 1 on success
+ * 0 on contention
*/
int __sched rt_mutex_trylock(struct rt_mutex *lock)
{
@@ -1508,7 +1459,14 @@ 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);
+ /*
+ * No lockdep annotation required because lockdep disables the fast
+ * path.
+ */
+ 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 +1482,26 @@ 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.
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