The manual says that it is required and we actually have crash reports
where loads see stale data due to not having membars here.

In one case the networking does:

	memset(skb, 0, offsetof(struct sk_buff, truesize));

and then some code later checks skb->nohdr for zero, but it's still
the value that was there before the memset().

Note that arch/sparc64/lib/xor.S already got this right.
Signed-off-by: David S. Miller <davem@davemloft.net>