diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/locking/rtmutex.c | 55 | ||||
| -rw-r--r-- | kernel/locking/rtmutex_api.c | 6 |
2 files changed, 49 insertions, 12 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 7779ee8abc2a..010cf4e6d0b8 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -89,15 +89,31 @@ static inline int __ww_mutex_check_kill(struct rt_mutex *lock, * set this bit before looking at the lock. */ -static __always_inline void -rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner) +static __always_inline struct task_struct * +rt_mutex_owner_encode(struct rt_mutex_base *lock, struct task_struct *owner) { unsigned long val = (unsigned long)owner; if (rt_mutex_has_waiters(lock)) val |= RT_MUTEX_HAS_WAITERS; - WRITE_ONCE(lock->owner, (struct task_struct *)val); + return (struct task_struct *)val; +} + +static __always_inline void +rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner) +{ + /* + * lock->wait_lock is held but explicit acquire semantics are needed + * for a new lock owner so WRITE_ONCE is insufficient. + */ + xchg_acquire(&lock->owner, rt_mutex_owner_encode(lock, owner)); +} + +static __always_inline void rt_mutex_clear_owner(struct rt_mutex_base *lock) +{ + /* lock->wait_lock is held so the unlock provides release semantics. */ + WRITE_ONCE(lock->owner, rt_mutex_owner_encode(lock, NULL)); } static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock) @@ -106,7 +122,8 @@ static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock) ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS); } -static __always_inline void fixup_rt_mutex_waiters(struct rt_mutex_base *lock) +static __always_inline void +fixup_rt_mutex_waiters(struct rt_mutex_base *lock, bool acquire_lock) { unsigned long owner, *p = (unsigned long *) &lock->owner; @@ -172,8 +189,21 @@ static __always_inline void fixup_rt_mutex_waiters(struct rt_mutex_base *lock) * still set. */ owner = READ_ONCE(*p); - if (owner & RT_MUTEX_HAS_WAITERS) - WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS); + if (owner & RT_MUTEX_HAS_WAITERS) { + /* + * See rt_mutex_set_owner() and rt_mutex_clear_owner() on + * why xchg_acquire() is used for updating owner for + * locking and WRITE_ONCE() for unlocking. + * + * WRITE_ONCE() would work for the acquire case too, but + * in case that the lock acquisition failed it might + * force other lockers into the slow path unnecessarily. + */ + if (acquire_lock) + xchg_acquire(p, owner & ~RT_MUTEX_HAS_WAITERS); + else + WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS); + } } /* @@ -208,6 +238,13 @@ static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock) owner = *p; } while (cmpxchg_relaxed(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner); + + /* + * The cmpxchg loop above is relaxed to avoid back-to-back ACQUIRE + * operations in the event of contention. Ensure the successful + * cmpxchg is visible. + */ + smp_mb__after_atomic(); } /* @@ -1243,7 +1280,7 @@ static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock) * try_to_take_rt_mutex() sets the lock waiters bit * unconditionally. Clean this up. */ - fixup_rt_mutex_waiters(lock); + fixup_rt_mutex_waiters(lock, true); return ret; } @@ -1604,7 +1641,7 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock, * try_to_take_rt_mutex() sets the waiter bit * unconditionally. We might have to fix that up. */ - fixup_rt_mutex_waiters(lock); + fixup_rt_mutex_waiters(lock, true); trace_contention_end(lock, ret); @@ -1719,7 +1756,7 @@ static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock) * try_to_take_rt_mutex() sets the waiter bit unconditionally. * We might have to fix that up: */ - fixup_rt_mutex_waiters(lock); + fixup_rt_mutex_waiters(lock, true); debug_rt_mutex_free_waiter(&waiter); trace_contention_end(lock, 0); diff --git a/kernel/locking/rtmutex_api.c b/kernel/locking/rtmutex_api.c index 900220941caa..cb9fdff76a8a 100644 --- a/kernel/locking/rtmutex_api.c +++ b/kernel/locking/rtmutex_api.c @@ -267,7 +267,7 @@ void __sched rt_mutex_init_proxy_locked(struct rt_mutex_base *lock, void __sched rt_mutex_proxy_unlock(struct rt_mutex_base *lock) { debug_rt_mutex_proxy_unlock(lock); - rt_mutex_set_owner(lock, NULL); + rt_mutex_clear_owner(lock); } /** @@ -382,7 +382,7 @@ int __sched rt_mutex_wait_proxy_lock(struct rt_mutex_base *lock, * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might * have to fix that up. */ - fixup_rt_mutex_waiters(lock); + fixup_rt_mutex_waiters(lock, true); raw_spin_unlock_irq(&lock->wait_lock); return ret; @@ -438,7 +438,7 @@ bool __sched rt_mutex_cleanup_proxy_lock(struct rt_mutex_base *lock, * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might * have to fix that up. */ - fixup_rt_mutex_waiters(lock); + fixup_rt_mutex_waiters(lock, false); raw_spin_unlock_irq(&lock->wait_lock); |