diff options
Diffstat (limited to 'kernel/locking/rwsem.c')
| -rw-r--r-- | kernel/locking/rwsem.c | 86 |
1 files changed, 74 insertions, 12 deletions
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 180455b6b0d4..985a03ad3f8c 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -458,6 +458,30 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem, #ifdef CONFIG_RWSEM_SPIN_ON_OWNER /* + * Try to acquire read lock before the reader is put on wait queue. + * Lock acquisition isn't allowed if the rwsem is locked or a writer handoff + * is ongoing. + */ +static inline bool rwsem_try_read_lock_unqueued(struct rw_semaphore *sem) +{ + long count = atomic_long_read(&sem->count); + + if (count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF)) + return false; + + count = atomic_long_fetch_add_acquire(RWSEM_READER_BIAS, &sem->count); + if (!(count & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) { + rwsem_set_reader_owned(sem); + lockevent_inc(rwsem_opt_rlock); + return true; + } + + /* Back out the change */ + atomic_long_add(-RWSEM_READER_BIAS, &sem->count); + return false; +} + +/* * Try to acquire write lock before the writer has been put on wait queue. */ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem) @@ -491,9 +515,12 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) BUILD_BUG_ON(is_rwsem_owner_spinnable(RWSEM_OWNER_UNKNOWN)); - if (need_resched()) + if (need_resched()) { + lockevent_inc(rwsem_opt_fail); return false; + } + preempt_disable(); rcu_read_lock(); owner = READ_ONCE(sem->owner); if (owner) { @@ -501,6 +528,9 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) owner_on_cpu(owner); } rcu_read_unlock(); + preempt_enable(); + + lockevent_cond_inc(rwsem_opt_fail, !ret); return ret; } @@ -578,7 +608,7 @@ static noinline enum owner_state rwsem_spin_on_owner(struct rw_semaphore *sem) return state; } -static bool rwsem_optimistic_spin(struct rw_semaphore *sem) +static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock) { bool taken = false; int prev_owner_state = OWNER_NULL; @@ -586,9 +616,6 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem) preempt_disable(); /* sem->wait_lock should not be held when doing optimistic spinning */ - if (!rwsem_can_spin_on_owner(sem)) - goto done; - if (!osq_lock(&sem->osq)) goto done; @@ -608,10 +635,11 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem) /* * Try to acquire the lock */ - if (rwsem_try_write_lock_unqueued(sem)) { - taken = true; + taken = wlock ? rwsem_try_write_lock_unqueued(sem) + : rwsem_try_read_lock_unqueued(sem); + + if (taken) break; - } /* * An RT task cannot do optimistic spinning if it cannot @@ -668,7 +696,12 @@ done: return taken; } #else -static bool rwsem_optimistic_spin(struct rw_semaphore *sem) +static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) +{ + return false; +} + +static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock) { return false; } @@ -684,6 +717,31 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int state) struct rwsem_waiter waiter; DEFINE_WAKE_Q(wake_q); + if (!rwsem_can_spin_on_owner(sem)) + goto queue; + + /* + * Undo read bias from down_read() and do optimistic spinning. + */ + atomic_long_add(-RWSEM_READER_BIAS, &sem->count); + adjustment = 0; + if (rwsem_optimistic_spin(sem, false)) { + /* + * Wake up other readers in the wait list if the front + * waiter is a reader. + */ + if ((atomic_long_read(&sem->count) & RWSEM_FLAG_WAITERS)) { + raw_spin_lock_irq(&sem->wait_lock); + if (!list_empty(&sem->wait_list)) + rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, + &wake_q); + raw_spin_unlock_irq(&sem->wait_lock); + wake_up_q(&wake_q); + } + return sem; + } + +queue: waiter.task = current; waiter.type = RWSEM_WAITING_FOR_READ; waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT; @@ -696,7 +754,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int state) * exit the slowpath and return immediately as its * RWSEM_READER_BIAS has already been set in the count. */ - if (!(atomic_long_read(&sem->count) & + if (adjustment && !(atomic_long_read(&sem->count) & (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) { raw_spin_unlock_irq(&sem->wait_lock); rwsem_set_reader_owned(sem); @@ -708,7 +766,10 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int state) list_add_tail(&waiter.list, &sem->wait_list); /* we're now waiting on the lock, but no longer actively locking */ - count = atomic_long_add_return(adjustment, &sem->count); + if (adjustment) + count = atomic_long_add_return(adjustment, &sem->count); + else + count = atomic_long_read(&sem->count); /* * If there are no active locks, wake the front queued process(es). @@ -767,7 +828,8 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state) DEFINE_WAKE_Q(wake_q); /* do optimistic spinning and steal lock if possible */ - if (rwsem_optimistic_spin(sem)) + if (rwsem_can_spin_on_owner(sem) && + rwsem_optimistic_spin(sem, true)) return sem; /* |