From e17ba59b7e8e1f67e36d8fcc46daa13370efcf11 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sun, 15 Aug 2021 23:28:12 +0200 Subject: [PATCH] locking/rtmutex: Guard regular sleeping locks specific functions 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 Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20210815211303.311535693@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(-) diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 8b0d38d..949781a 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1075,10 +1075,139 @@ static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh, raw_spin_unlock(¤t->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_lock(struct rt_mutex_base *lock, 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 */ diff --git a/kernel/locking/rtmutex_api.c b/kernel/locking/rtmutex_api.c index 56403dc..7f3ac09 100644 --- a/kernel/locking/rtmutex_api.c +++ b/kernel/locking/rtmutex_api.c @@ -5,6 +5,7 @@ #include #include +#define RT_MUTEX_BUILD_MUTEX #include "rtmutex.c" /* diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index c017f9f..2847833 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -1347,6 +1347,7 @@ static inline void __downgrade_write(struct rw_semaphore *sem) #else /* !CONFIG_PREEMPT_RT */ +#define RT_MUTEX_BUILD_MUTEX #include "rtmutex.c" #define rwbase_set_and_save_current_state(state) \ -- 2.7.4