On 2024-11-12 08:52:11 [-1000], Tejun Heo wrote:
> Hello,
Hi,
> On Tue, Nov 12, 2024 at 04:52:38PM +0100, Sebastian Andrzej Siewior wrote:
> ...
> > KERNFS_ROOT_SAME_PARENT is added to signal that the parent never
>
> Maybe KERNFS_ROOT_INVARIANT_PARENT captures it better?
Sure.
> ...
> > @@ -195,13 +191,47 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
> > */
> > int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
> > {
> > + struct kernfs_root *root;
> >
> > + guard(read_lock_irqsave)(&kernfs_rename_lock);
> > + if (kn) {
> > + root = kernfs_root(kn);
> > + if (WARN_ON_ONCE(root->flags & KERNFS_ROOT_SAME_PARENT))
> > + kn = NULL;
>
> Hmm... does kn need to be set to NULL here?
actually no, because read_lock() implies RCU protection.
> > + }
> > +
> > + if (!kn)
> > + return strscpy(buf, "(null)", buflen);
> > +
> > + return strscpy(buf, kn->parent ? kn->name : "/", buflen);
> ...
> > +int kernfs_name_rcu(struct kernfs_node *kn, char *buf, size_t buflen)
> > +{
> > + struct kernfs_root *root;
> > +
> > + if (kn) {
> > + root = kernfs_root(kn);
> > + if (WARN_ON_ONCE(!(root->flags & KERNFS_ROOT_SAME_PARENT)))
> > + kn = NULL;
>
> Ah, I suppose it's to keep things symmetric. That's fine.
>
> > + }
> > + if (!kn)
> > + return strscpy(buf, "(null)", buflen);
> > +
> > + guard(rcu)();
>
> Also, why are guards in different locations? Even when !SAME_PARENT, kn's
> can't jump across roots, so guard there can also be in the same location as
> this one?
I tried to limit the scope but it can be symmetrical.
> ...
> > @@ -200,7 +205,10 @@ struct kernfs_node {
> > * parent directly.
> > */
> > struct kernfs_node *parent;
> > - const char *name;
> > + union {
> > + const char __rcu *name_rcu;
> > + const char *name;
> > + };
>
> Wouldn't it be simpler if ->name is always __rcu and !SAME_PARENT just
> requires further protection on the read side?
Let me try that again.
> Thanks.
>
Sebastian
