26  * - try-lock semantics for readers and writers
33  * __btrfs_tree_read_lock - lock extent buffer for read
37  * This takes the read lock on the extent buffer, using the specified nesting
47 	down_read_nested(&eb->lock, nest);  in __btrfs_tree_read_lock()
58  * Try-lock for read.
64 	if (down_read_trylock(&eb->lock)) {  in btrfs_try_tree_read_lock()
73  * Try-lock for write.
79 	if (down_write_trylock(&eb->lock)) {  in btrfs_try_tree_write_lock()
88  * Release read lock.
94 	up_read(&eb->lock);  in btrfs_tree_read_unlock()
98  * __btrfs_tree_lock - lock eb for write
99  * @eb:		the eb to lock
100  * @nest:	the nesting to use for the lock
102  * Returns with the eb->lock write locked.
105 	__acquires(&eb->lock)  in __btrfs_tree_lock()
112 	down_write_nested(&eb->lock, nest);  in __btrfs_tree_lock()
123  * Release the write lock.
129 	up_write(&eb->lock);  in btrfs_tree_unlock()
136  * btrfs_search_slot will keep the lock held on higher nodes in a few corner
160  * we end up with a lock on the root node.
162  * Return: root extent buffer with write lock held
181  * we end up with a lock on the root node.
183  * Return: root extent buffer with read lock held
204  * DREW stands for double-reader-writer-exclusion lock. It's used in situation
208  * writer both race to acquire their respective sides of the lock the writer
209  * would yield its lock as soon as it detects a concurrent reader. Additionally
211  * acquire the lock.
214 int btrfs_drew_lock_init(struct btrfs_drew_lock *lock)  in btrfs_drew_lock_init()  argument
218 	ret = percpu_counter_init(&lock->writers, 0, GFP_KERNEL);  in btrfs_drew_lock_init()
222 	atomic_set(&lock->readers, 0);  in btrfs_drew_lock_init()
223 	init_waitqueue_head(&lock->pending_readers);  in btrfs_drew_lock_init()
224 	init_waitqueue_head(&lock->pending_writers);  in btrfs_drew_lock_init()
229 void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock)  in btrfs_drew_lock_destroy()  argument
231 	percpu_counter_destroy(&lock->writers);  in btrfs_drew_lock_destroy()
235 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock)  in btrfs_drew_try_write_lock()  argument
237 	if (atomic_read(&lock->readers))  in btrfs_drew_try_write_lock()
240 	percpu_counter_inc(&lock->writers);  in btrfs_drew_try_write_lock()
244 	if (atomic_read(&lock->readers)) {  in btrfs_drew_try_write_lock()
245 		btrfs_drew_write_unlock(lock);  in btrfs_drew_try_write_lock()
252 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock)  in btrfs_drew_write_lock()  argument
255 		if (btrfs_drew_try_write_lock(lock))  in btrfs_drew_write_lock()
257 		wait_event(lock->pending_writers, !atomic_read(&lock->readers));  in btrfs_drew_write_lock()
261 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock)  in btrfs_drew_write_unlock()  argument
263 	percpu_counter_dec(&lock->writers);  in btrfs_drew_write_unlock()
264 	cond_wake_up(&lock->pending_readers);  in btrfs_drew_write_unlock()
267 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock)  in btrfs_drew_read_lock()  argument
269 	atomic_inc(&lock->readers);  in btrfs_drew_read_lock()
279 	wait_event(lock->pending_readers,  in btrfs_drew_read_lock()
280 		   percpu_counter_sum(&lock->writers) == 0);  in btrfs_drew_read_lock()
283 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock)  in btrfs_drew_read_unlock()  argument
289 	if (atomic_dec_and_test(&lock->readers))  in btrfs_drew_read_unlock()
290 		wake_up(&lock->pending_writers);  in btrfs_drew_read_unlock()