I think the expected way to zero is kzalloc():
https://www.kernel.org/doc/htmldocs/kernel-api/API-kzalloc.html
but obviously alloc + memset works too.
Update
Sample diff from CFQ showing the expected updates:
- cfqd = kmalloc_node(sizeof(*cfqd), GFP_KERNEL | __GFP_ZERO, q->node);
+ cfqd = kzalloc_node(sizeof(*cfqd), GFP_KERNEL, q->node);
See also this: https://stackoverflow.com/a/12095263/2908724