ceph: avoid iput() while holding spinlock in ceph_dir_fsync

ceph_mdsc_put_request() can call iput(), which can sleep.  Don't do that.

Fixes: #1812
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/dir.c

@@ -1218,6 +1218,7 @@ static int ceph_dir_fsync(struct file *file, loff_t start, loff_t end,
 	do {
 		ceph_mdsc_get_request(req);
 		spin_unlock(&ci->i_unsafe_lock);
+
 		dout("dir_fsync %p wait on tid %llu (until %llu)\n",
 		     inode, req->r_tid, last_tid);
 		if (req->r_timeout) {
@@ -1230,9 +1231,9 @@ static int ceph_dir_fsync(struct file *file, loff_t start, loff_t end,
 		} else {
 			wait_for_completion(&req->r_safe_completion);
 		}
-		spin_lock(&ci->i_unsafe_lock);
 		ceph_mdsc_put_request(req);
 
+		spin_lock(&ci->i_unsafe_lock);
 		if (ret || list_empty(head))
 			break;
 		req = list_entry(head->next,