3 files changed, 9 insertions, 33 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 991ff26fb8c6..1b1b9e8197d6 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1341,17 +1341,8 @@ struct btrfs_root *btrfs_read_tree_root(struct btrfs_root *tree_root,
 static int btrfs_init_fs_root(struct btrfs_root *root, dev_t anon_dev)
 {
 	int ret;
-	unsigned int nofs_flag;
 
-	/*
-	 * We might be called under a transaction (e.g. indirect backref
-	 * resolution) which could deadlock if it triggers memory reclaim
-	 */
-	nofs_flag = memalloc_nofs_save();
-	ret = btrfs_drew_lock_init(&root->snapshot_lock);
-	memalloc_nofs_restore(nofs_flag);
-	if (ret)
-		goto fail;
+	btrfs_drew_lock_init(&root->snapshot_lock);
 
 	if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID &&
 	    !btrfs_is_data_reloc_root(root)) {
@@ -2065,7 +2056,6 @@ void btrfs_put_root(struct btrfs_root *root)
 		WARN_ON(test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state));
 		if (root->anon_dev)
 			free_anon_bdev(root->anon_dev);
-		btrfs_drew_lock_destroy(&root->snapshot_lock);
 		free_root_extent_buffers(root);
 #ifdef CONFIG_BTRFS_DEBUG
 		spin_lock(&root->fs_info->fs_roots_radix_lock);
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 870528d87526..3a496b0d3d2b 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -325,24 +325,12 @@ struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root)
  * acquire the lock.
  */
 
-int btrfs_drew_lock_init(struct btrfs_drew_lock *lock)
+void btrfs_drew_lock_init(struct btrfs_drew_lock *lock)
 {
-	int ret;
-
-	ret = percpu_counter_init(&lock->writers, 0, GFP_KERNEL);
-	if (ret)
-		return ret;
-
 	atomic_set(&lock->readers, 0);
+	atomic_set(&lock->writers, 0);
 	init_waitqueue_head(&lock->pending_readers);
 	init_waitqueue_head(&lock->pending_writers);
-
-	return 0;
-}
-
-void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock)
-{
-	percpu_counter_destroy(&lock->writers);
 }
 
 /* Return true if acquisition is successful, false otherwise */
@@ -351,10 +339,10 @@ bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock)
 	if (atomic_read(&lock->readers))
 		return false;
 
-	percpu_counter_inc(&lock->writers);
+	atomic_inc(&lock->writers);
 
 	/* Ensure writers count is updated before we check for pending readers */
-	smp_mb();
+	smp_mb__after_atomic();
 	if (atomic_read(&lock->readers)) {
 		btrfs_drew_write_unlock(lock);
 		return false;
@@ -374,7 +362,7 @@ void btrfs_drew_write_lock(struct btrfs_drew_lock *lock)
 
 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock)
 {
-	percpu_counter_dec(&lock->writers);
+	atomic_dec(&lock->writers);
 	cond_wake_up(&lock->pending_readers);
 }
 
@@ -390,8 +378,7 @@ void btrfs_drew_read_lock(struct btrfs_drew_lock *lock)
 	 */
 	smp_mb__after_atomic();
 
-	wait_event(lock->pending_readers,
-		   percpu_counter_sum(&lock->writers) == 0);
+	wait_event(lock->pending_readers, atomic_read(&lock->writers) == 0);
 }
 
 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock)
diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h
index 11c2269b4b6f..edb9b4a0dba1 100644
--- a/fs/btrfs/locking.h
+++ b/fs/btrfs/locking.h
@@ -195,13 +195,12 @@ static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw)
 
 struct btrfs_drew_lock {
 	atomic_t readers;
-	struct percpu_counter writers;
+	atomic_t writers;
 	wait_queue_head_t pending_writers;
 	wait_queue_head_t pending_readers;
 };
 
-int btrfs_drew_lock_init(struct btrfs_drew_lock *lock);
-void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock);
+void btrfs_drew_lock_init(struct btrfs_drew_lock *lock);
 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock);
 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock);
 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock);