Deadlock between nfsd and snapshots.

[Tor Egge]

> Does this mean that setting the noatime flag on mount would dodge this?

It might solve the deadlock issue when creating snapshots.  Note that snapshots
might fail to make copies of the original content when file system metadata
changes on some systems (cf. PR kern/100365).

Setting the noatime flag does not prevent ufs_itimes() from changing the inode
flags without proper locking.  IN_CHANGE might be set on the inode after a
chmod() system call, a following fstat() system call can then trigger a call to
ufs_itimes().

- Tor Egge