Hi,
Nick Piggin:
> Thanks for your help, can you see how I've fixed it in my vfs-scale
> tree? What do you think?
Your fix is great. I have no objection at all.
Other than the fix, here are more generic questions about vfs-scale work.
I am happy if you reply when you have time.
- getcwd(2) needs d_lock?
It acquires rename_lock and then tests whether the pwd is removed by
d_unhashed(). If a race condition between vfs_rename_dir() which may
unhash/rehash the dentry happens, then getcwd() may return the wrong
result due to unprotected d_unhashed() call, I am afraid. rename_lock
doesn't help this case.
- what is the right order of dget() and mntget()?
If I remember correctly, someone said "mntget() first and then
dget(). when putting, do in reverse" in the discussion when
path_{get,put}() were born. So it is called "the right order" in the
commit log.
It was many years ago. Is it still true? And should rcu-walk follow it
too? The current implementation doesn't seem to care about this order.
- d_move() and rename_lock
This may be out of rcu-walk work, but rename_lock in d_move() looks
outstanding since it surely kills concurrency. It is a pity that two
unrelated but concurrent d_move-s are serialized when we run rename(2)
on two different filesystems. Even if all of dentries, parents and
hash buckets are different from each other, d_move() never run
concurrently.
J. R. Okajima
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