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_nested - 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);
151  * Try-lock for read.
157 	if (down_read_trylock(&eb->lock)) {
165  * Try-lock for write.
171 	if (down_write_trylock(&eb->lock)) {
180  * Release read lock.
185 	up_read(&eb->lock);
191  * @eb:		the eb to lock
192  * @nest:	the nesting to use for the lock
194  * Returns with the eb->lock write locked.
197 	__acquires(&eb->lock)
204 	down_write_nested(&eb->lock, nest);
210  * Release the write lock.
216 	up_write(&eb->lock);
223  * btrfs_search_slot will keep the lock held on higher nodes in a few corner
247  * we end up with a lock on the root node.
249  * Return: root extent buffer with write lock held
270  * we end up with a lock on the root node.
272  * Return: root extent buffer with read lock held
293  * nowait mode until we end up with a lock on the root node or returning to
296  * Return: root extent buffer with read lock held or -EAGAIN.
320  * DREW stands for double-reader-writer-exclusion lock. It's used in situation
324  * writer both race to acquire their respective sides of the lock the writer
325  * would yield its lock as soon as it detects a concurrent reader. Additionally
327  * acquire the lock.
330 void btrfs_drew_lock_init(struct btrfs_drew_lock *lock)
332 	atomic_set(&lock->readers, 0);
333 	atomic_set(&lock->writers, 0);
334 	init_waitqueue_head(&lock->pending_readers);
335 	init_waitqueue_head(&lock->pending_writers);
339 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock)
341 	if (atomic_read(&lock->readers))
344 	atomic_inc(&lock->writers);
348 	if (atomic_read(&lock->readers)) {
349 		btrfs_drew_write_unlock(lock);
356 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock)
359 		if (btrfs_drew_try_write_lock(lock))
361 		wait_event(lock->pending_writers, !atomic_read(&lock->readers));
365 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock)
371 	if (atomic_dec_and_test(&lock->writers))
372 		wake_up(&lock->pending_readers);
375 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock)
377 	atomic_inc(&lock->readers);
387 	wait_event(lock->pending_readers, atomic_read(&lock->writers) == 0);
390 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock)
396 	if (atomic_dec_and_test(&lock->readers))
397 		wake_up(&lock->pending_writers);