input/output error @boot

[Dexuan Cui]

> From: Dexuan Cui
> I committed r314770 just now to minimize the impact:
> https://svnweb.freebsd.org/base?view=revision&revision=314770
> 
> Please let me know in case this can't solve the issue.
 
Sorry, r314770  has a bug, so I had to commit r314828:
https://svnweb.freebsd.org/base?view=revision&revision=314828

Please make sure you use the latest code, i.e. >= r314828.

Thanks,
-- Dexuan