[patch V3 22/64] locking/rtmutex: Guard regular sleeping locks specific functions

Thomas Gleixner
2021-08-05T15:42:50Z

From: Thomas Gleixner <tglx@linutronix.de>

Guard the regular sleeping lock specific functionality which is used for
rtmutex on non-RT enabled kernels and for mutex, rtmutex and semaphores on
RT enabled kernels so the code can be reused for the RT specific
implementation of spinlocks and rwlocks in a different compilation unit.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/locking/rtmutex.c | 254 ++++++++++++++++++++++---------------------
kernel/locking/rtmutex_api.c | 1
kernel/locking/rwsem.c | 1
3 files changed, 133 insertions(+), 123 deletions(-)
---
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1075,10 +1075,139 @@ static void __sched mark_wakeup_next_wai
raw_spin_unlock(&current->pi_lock);
}

+static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock)
+{
+ int ret = try_to_take_rt_mutex(lock, current, NULL);
+
+ /*
+ * try_to_take_rt_mutex() sets the lock waiters bit
+ * unconditionally. Clean this up.
+ */
+ fixup_rt_mutex_waiters(lock);
+
+ return ret;
+}
+
+/*
+ * Slow path try-lock function:
+ */
+static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock)
+{
+ unsigned long flags;
+ int ret;
+
+ /*
+ * If the lock already has an owner we fail to get the lock.
+ * This can be done without taking the @lock->wait_lock as
+ * it is only being read, and this is a trylock anyway.
+ */
+ if (rt_mutex_owner(lock))
+ return 0;
+
+ /*
+ * The mutex has currently no owner. Lock the wait lock and try to
+ * acquire the lock. We use irqsave here to support early boot calls.
+ */
+ raw_spin_lock_irqsave(&lock->wait_lock, flags);
+
+ ret = __rt_mutex_slowtrylock(lock);
+
+ raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+
+ return ret;
+}
+
+static __always_inline int __rt_mutex_trylock(struct rt_mutex_base *lock)
+{
+ if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
+ return 1;
+
+ return rt_mutex_slowtrylock(lock);
+}
+
+/*
+ * Slow path to release a rt-mutex.
+ */
+static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
+{
+ DEFINE_RT_WAKE_Q(wqh);
+ unsigned long flags;
+
+ /* irqsave required to support early boot calls */
+ raw_spin_lock_irqsave(&lock->wait_lock, flags);
+
+ debug_rt_mutex_unlock(lock);
+
+ /*
+ * We must be careful here if the fast path is enabled. If we
+ * have no waiters queued we cannot set owner to NULL here
+ * because of:
+ *
+ * foo->lock->owner = NULL;
+ * rtmutex_lock(foo->lock); <- fast path
+ * free = atomic_dec_and_test(foo->refcnt);
+ * rtmutex_unlock(foo->lock); <- fast path
+ * if (free)
+ * kfree(foo);
+ * raw_spin_unlock(foo->lock->wait_lock);
+ *
+ * So for the fastpath enabled kernel:
+ *
+ * Nothing can set the waiters bit as long as we hold
+ * lock->wait_lock. So we do the following sequence:
+ *
+ * owner = rt_mutex_owner(lock);
+ * clear_rt_mutex_waiters(lock);
+ * raw_spin_unlock(&lock->wait_lock);
+ * if (cmpxchg(&lock->owner, owner, 0) == owner)
+ * return;
+ * goto retry;
+ *
+ * The fastpath disabled variant is simple as all access to
+ * lock->owner is serialized by lock->wait_lock:
+ *
+ * lock->owner = NULL;
+ * raw_spin_unlock(&lock->wait_lock);
+ */
+ while (!rt_mutex_has_waiters(lock)) {
+ /* Drops lock->wait_lock ! */
+ if (unlock_rt_mutex_safe(lock, flags) == true)
+ return;
+ /* Relock the rtmutex and try again */
+ raw_spin_lock_irqsave(&lock->wait_lock, flags);
+ }
+
+ /*
+ * The wakeup next waiter path does not suffer from the above
+ * race. See the comments there.
+ *
+ * Queue the next waiter for wakeup once we release the wait_lock.
+ */
+ mark_wakeup_next_waiter(&wqh, lock);
+ raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+
+ rt_mutex_wake_up_q(&wqh);
+}
+
+static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock)
+{
+ if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
+ return;
+
+ rt_mutex_slowunlock(lock);
+}
+
+#ifdef RT_MUTEX_BUILD_MUTEX
+/*
+ * Functions required for:
+ * - rtmutex, futex on all kernels
+ * - mutex and rwsem substitutions on RT kernels
+ */
+
/*
* Remove a waiter from a lock and give up
*
- * Must be called with lock->wait_lock held and interrupts disabled. I must
+ * Must be called with lock->wait_lock held and interrupts disabled. It must
* have just failed to try_to_take_rt_mutex().
*/
static void __sched remove_waiter(struct rt_mutex_base *lock,
@@ -1286,125 +1415,4 @@ static __always_inline int __rt_mutex_lo

return rt_mutex_slowlock(lock, state);
}
-
-static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock)
-{
- int ret = try_to_take_rt_mutex(lock, current, NULL);
-
- /*
- * try_to_take_rt_mutex() sets the lock waiters bit
- * unconditionally. Clean this up.
- */
- fixup_rt_mutex_waiters(lock);
-
- return ret;
-}
-
-/*
- * Slow path try-lock function:
- */
-static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock)
-{
- unsigned long flags;
- int ret;
-
- /*
- * If the lock already has an owner we fail to get the lock.
- * This can be done without taking the @lock->wait_lock as
- * it is only being read, and this is a trylock anyway.
- */
- if (rt_mutex_owner(lock))
- return 0;
-
- /*
- * The mutex has currently no owner. Lock the wait lock and try to
- * acquire the lock. We use irqsave here to support early boot calls.
- */
- raw_spin_lock_irqsave(&lock->wait_lock, flags);
-
- ret = __rt_mutex_slowtrylock(lock);
-
- raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
-
- return ret;
-}
-
-static __always_inline int __rt_mutex_trylock(struct rt_mutex_base *lock)
-{
- if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
- return 1;
-
- return rt_mutex_slowtrylock(lock);
-}
-
-/*
- * Slow path to release a rt-mutex.
- */
-static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
-{
- DEFINE_RT_WAKE_Q(wqh);
- unsigned long flags;
-
- /* irqsave required to support early boot calls */
- raw_spin_lock_irqsave(&lock->wait_lock, flags);
-
- debug_rt_mutex_unlock(lock);
-
- /*
- * We must be careful here if the fast path is enabled. If we
- * have no waiters queued we cannot set owner to NULL here
- * because of:
- *
- * foo->lock->owner = NULL;
- * rtmutex_lock(foo->lock); <- fast path
- * free = atomic_dec_and_test(foo->refcnt);
- * rtmutex_unlock(foo->lock); <- fast path
- * if (free)
- * kfree(foo);
- * raw_spin_unlock(foo->lock->wait_lock);
- *
- * So for the fastpath enabled kernel:
- *
- * Nothing can set the waiters bit as long as we hold
- * lock->wait_lock. So we do the following sequence:
- *
- * owner = rt_mutex_owner(lock);
- * clear_rt_mutex_waiters(lock);
- * raw_spin_unlock(&lock->wait_lock);
- * if (cmpxchg(&lock->owner, owner, 0) == owner)
- * return;
- * goto retry;
- *
- * The fastpath disabled variant is simple as all access to
- * lock->owner is serialized by lock->wait_lock:
- *
- * lock->owner = NULL;
- * raw_spin_unlock(&lock->wait_lock);
- */
- while (!rt_mutex_has_waiters(lock)) {
- /* Drops lock->wait_lock ! */
- if (unlock_rt_mutex_safe(lock, flags) == true)
- return;
- /* Relock the rtmutex and try again */
- raw_spin_lock_irqsave(&lock->wait_lock, flags);
- }
-
- /*
- * The wakeup next waiter path does not suffer from the above
- * race. See the comments there.
- *
- * Queue the next waiter for wakeup once we release the wait_lock.
- */
- mark_wakeup_next_waiter(&wqh, lock);
- raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
-
- rt_mutex_wake_up_q(&wqh);
-}
-
-static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock)
-{
- if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
- return;
-
- rt_mutex_slowunlock(lock);
-}
+#endif /* RT_MUTEX_BUILD_MUTEX */
--- a/kernel/locking/rtmutex_api.c
+++ b/kernel/locking/rtmutex_api.c
@@ -5,6 +5,7 @@
#include <linux/spinlock.h>
#include <linux/export.h>

+#define RT_MUTEX_BUILD_MUTEX
#include "rtmutex.c"

/*
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1347,6 +1347,7 @@ static inline void __downgrade_write(str

#else /* !CONFIG_PREEMPT_RT */

+#define RT_MUTEX_BUILD_MUTEX
#include "rtmutex.c"

#define rwbase_set_and_save_current_state(state) \