Btrfs: do not pin while under spin lock

When testing a corrupted fs I noticed I was getting sleep while atomic errors
when the transaction aborted.  This is because btrfs_pin_extent may need to
allocate memory and we are calling this under the spin lock.  Fix this by moving
it out and doing the pin after dropping the spin lock but before dropping the
mutex, the same way it works when delayed refs run normally.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/disk-io.c

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 9b70201..3c2886c 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3762,6 +3762,7 @@
 
 	while ((node = rb_first(&delayed_refs->root)) != NULL) {
 		struct btrfs_delayed_ref_head *head = NULL;
+		bool pin_bytes = false;
 
 		ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
 		atomic_set(&ref->refs, 1);
@@ -3782,8 +3783,7 @@
 			}
 
 			if (head->must_insert_reserved)
-				btrfs_pin_extent(root, ref->bytenr,
-						 ref->num_bytes, 1);
+				pin_bytes = true;
 			btrfs_free_delayed_extent_op(head->extent_op);
 			delayed_refs->num_heads--;
 			if (list_empty(&head->cluster))
@@ -3794,9 +3794,13 @@
 		ref->in_tree = 0;
 		rb_erase(&ref->rb_node, &delayed_refs->root);
 		delayed_refs->num_entries--;
-		if (head)
-			mutex_unlock(&head->mutex);
 		spin_unlock(&delayed_refs->lock);
+		if (head) {
+			if (pin_bytes)
+				btrfs_pin_extent(root, ref->bytenr,
+						 ref->num_bytes, 1);
+			mutex_unlock(&head->mutex);
+		}
 		btrfs_put_delayed_ref(ref);
 
 		cond_resched();