fs/btrfs/locking.c

18  * Lockdep class keys for extent_buffer->lock's in this root.  For a given
94 	lockdep_set_class_and_name(&eb->lock, &ks->keys[level], ks->names[level]);
125  * - try-lock semantics for readers and writers
132  * __btrfs_tree_read_lock - lock extent buffer for read
136  * This takes the read lock on the extent buffer, using the specified nesting
146 	down_read_nested(&eb->lock, nest);
156  * Try-lock for read.
162 	if (down_read_trylock(&eb->lock)) {
170  * Try-lock for write.
176 	if (down_write_trylock(&eb->lock)) {
185  * Release read lock.
190 	up_read(&eb->lock);
196  * @eb:		the eb to lock
197  * @nest:	the nesting to use for the lock
199  * Returns with the eb->lock write locked.
202 	__acquires(&eb->lock)
209 	down_write_nested(&eb->lock, nest);
220  * Release the write lock.
226 	up_write(&eb->lock);
233  * btrfs_search_slot will keep the lock held on higher nodes in a few corner
257  * we end up with a lock on the root node.
259  * Return: root extent buffer with write lock held
280  * we end up with a lock on the root node.
282  * Return: root extent buffer with read lock held
303  * nowait mode until we end up with a lock on the root node or returning to
306  * Return: root extent buffer with read lock held or -EAGAIN.
330  * DREW stands for double-reader-writer-exclusion lock. It's used in situation
334  * writer both race to acquire their respective sides of the lock the writer
335  * would yield its lock as soon as it detects a concurrent reader. Additionally
337  * acquire the lock.
340 void btrfs_drew_lock_init(struct btrfs_drew_lock *lock)
342 	atomic_set(&lock->readers, 0);
343 	atomic_set(&lock->writers, 0);
344 	init_waitqueue_head(&lock->pending_readers);
345 	init_waitqueue_head(&lock->pending_writers);
349 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock)
351 	if (atomic_read(&lock->readers))
354 	atomic_inc(&lock->writers);
358 	if (atomic_read(&lock->readers)) {
359 		btrfs_drew_write_unlock(lock);
366 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock)
369 		if (btrfs_drew_try_write_lock(lock))
371 		wait_event(lock->pending_writers, !atomic_read(&lock->readers));
375 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock)
377 	atomic_dec(&lock->writers);
378 	cond_wake_up(&lock->pending_readers);
381 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock)
383 	atomic_inc(&lock->readers);
393 	wait_event(lock->pending_readers, atomic_read(&lock->writers) == 0);
396 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock)
402 	if (atomic_dec_and_test(&lock->readers))
403 		wake_up(&lock->pending_writers);