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由 Al Viro 提交于
Otherwise we are risking a hard error where nonlazy restart would be the right thing to do; it's a very narrow race with mount --move and most of the time it ends up being completely harmless, but it's possible to construct a case when we'll get a bogus hard error instead of falling back to non-lazy walk... For one thing, when crossing _into_ overmount of parent we need to check for mount_lock bumps when we get NULL from __lookup_mnt() as well. For another, and less exotically, we need to make sure that the data fetched in follow_up_rcu() had been consistent. ->mnt_mountpoint is pinned for as long as it is a mountpoint, but we need to check mount_lock after fetching to verify that. Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
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