Re: vfs-scale, general questions (Re: NFS root lockups with -next 20110113)

[J. R. Okajima]

Ian Kent:
> > - 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.
>
> I didn't spot that, where did you see this?
>
> I'm not sure about the get but I fairly sure the dput() has to be before
> the mntput() because the shrink_dcache_*() cleanup routines object to
> dentrys that have a reference count of more than one.

For dget - mntget, there are several such code. For example,
nameidata_dentry_drop_rcu()
{
	struct dentry *parent = nd->path.dentry;
		:::
	parent->d_count++;
	spin_unlock(&dentry->d_lock);
	spin_unlock(&parent->d_lock);
		:::
	mntget(nd->path.mnt);
		:::

But I am not sure the "get" order is a problem.
Nick Piggin also replied and said dget and mntget is not a problem, and
I replied if I found such "put" order, I would write again.


J. R. Okajima
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