/*
* queue_read_lock_slowpath - acquire read lock of a queue rwlock.
* @lock: Pointer to queue rwlock structure.
*/
void queue_read_lock_slowpath(rwlock_t *lock)
{
u32 cnts;
/*
* Readers come here when they cannot get the lock without waiting.
*/
atomic_sub(_QR_BIAS, &lock->cnts);
/*
* Put the reader into the wait queue.
*/
spin_lock(&lock->lock);
/*
* At the head of the wait queue now, wait until the writer state
* goes to 0 and then try to increment the reader count and get
* the lock. It is possible that an incoming writer may steal the
* lock in the interim, so it is necessary to check the writer byte
* to make sure that the write lock isn't taken.
*/
while ( atomic_read(&lock->cnts) & _QW_WMASK )
cpu_relax();
cnts = atomic_add_return(_QR_BIAS, &lock->cnts) - _QR_BIAS;
rspin_until_writer_unlock(lock, cnts);
/*
* Signal the next one in queue to become queue head.
*/
spin_unlock(&lock->lock);
}
/**
* queued_read_lock_slowpath - acquire read lock of a queue rwlock
* @lock: Pointer to queue rwlock structure
* @cnts: Current qrwlock lock value
*/
void queued_read_lock_slowpath(struct qrwlock *lock, u32 cnts)
{
/*
* Readers come here when they cannot get the lock without waiting
*/
if (unlikely(in_interrupt())) {
/*
* Readers in interrupt context will get the lock immediately
* if the writer is just waiting (not holding the lock yet).
* The rspin_until_writer_unlock() function returns immediately
* in this case. Otherwise, they will spin (with ACQUIRE
* semantics) until the lock is available without waiting in
* the queue.
*/
rspin_until_writer_unlock(lock, cnts);
return;
}
atomic_sub(_QR_BIAS, &lock->cnts);
/*
* Put the reader into the wait queue
*/
arch_spin_lock(&lock->lock);
/*
* The ACQUIRE semantics of the following spinning code ensure
* that accesses can't leak upwards out of our subsequent critical
* section in the case that the lock is currently held for write.
*/
cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts) - _QR_BIAS;
rspin_until_writer_unlock(lock, cnts);
/*
* Signal the next one in queue to become queue head
*/
arch_spin_unlock(&lock->lock);
}
