fuse: avoid unnecessary spinlock bump

Move dmap free worker kicker inside the critical region, so that extra
spinlock lock/unlock could be avoided.
Suggested-by: Liu Jiang <gerry@linux.alibaba.com>
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dax.c

@@ -138,9 +138,9 @@ static struct fuse_dax_mapping *alloc_dax_mapping(struct fuse_conn_dax *fcd)
 		WARN_ON(fcd->nr_free_ranges <= 0);
 		fcd->nr_free_ranges--;
 	}
+	__kick_dmap_free_worker(fcd, 0);
 	spin_unlock(&fcd->lock);
 
-	kick_dmap_free_worker(fcd, 0);
 	return dmap;
 }