On Mar 10, 2016, at 12:15 AM, Al Viro wrote:
> PS: there's a reason why e.g. NFS ->d_revalidate() is doing
> if (flags & LOOKUP_RCU) {
> parent = ACCESS_ONCE(dentry->d_parent);
> dir = d_inode_rcu(parent);
> if (!dir)
> return -ECHILD;
> } else {
> parent = dget_parent(dentry);
> dir = d_inode(parent);
> }
> and so do other instances. It does *not* guarantee that parent will remain
> the parent through the whole thing (or will still be one by the time
> dget_parent() caller gets the return value), but it does guarantee that it
> won't get freed under you. Note that the original parent won't disappear
> (it's pinned by the caller), but there's no promise that what you'll
> fetch from dentry->d_parent inside the method will have anything to do with
> that.
>
> BTW, we might be better off if we passed the parent and child as separate
> arguments…
I wonder if this is something you are seriously contemplating doing or should
I still future-proof Lustre a bit and get a patch going to use dget_parent/dput
in ll_revalidate_dentry in Lustre?
While it's not a problem now due to the external locking, that might change
in the future--
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