Messages in this thread | | | Date | Thu, 5 May 2022 10:01:51 -1000 | From | Tejun Heo <> | Subject | Re: [PATCH 2/5] kernfs: make ->attr.open RCU protected. |
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On Thu, Apr 28, 2022 at 03:54:28PM +1000, Imran Khan wrote: > +static struct kernfs_open_node *kernfs_deref_on_raw(struct kernfs_node *kn) > +{ > + return rcu_dereference_raw(kn->attr.open); > +}
Wrapping the above probably isn't helping anything.
> +/* > + * Check ->attr.open corresponding to @kn while holding kernfs_open_file_mutex. > + * ->attr.open is modified under kernfs_open_file_mutex. So it can be safely > + * accessed outside RCU read-side critical section, while holding the mutex. > + */ > +static struct kernfs_open_node *kernfs_check_on_protected(struct kernfs_node *kn) > +{ > + return rcu_dereference_check(kn->attr.open, > + lockdep_is_held(&kernfs_open_file_mutex)); > +}
Maybe name this just kernfs_deref_on()?
> @@ -156,8 +188,9 @@ static void kernfs_seq_stop(struct seq_file *sf, void *v) > static int kernfs_seq_show(struct seq_file *sf, void *v) > { > struct kernfs_open_file *of = sf->private; > + struct kernfs_open_node *on = kernfs_deref_on_raw(of->kn);
I suppose this is protected by the fact that @of is on @on? If so, just add the condition to the checked version. The condition doesn't have to be perfect - e.g. you can just say that neither @on's and @of's list_head isn't empty. While not comprehensive, it'd still provide meaningful protection against mistakes and be easier to understand if the deref accessor clearly explains the expectations.
> @@ -201,7 +235,8 @@ static ssize_t kernfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter) > goto out_free; > } > > - of->event = atomic_read(&of->kn->attr.open->event); > + on = kernfs_deref_on_raw(of->kn); > + of->event = atomic_read(&unrcu_pointer(on)->event);
Ditto here.
> @@ -815,7 +843,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn) > __poll_t kernfs_generic_poll(struct kernfs_open_file *of, poll_table *wait) > { > struct kernfs_node *kn = kernfs_dentry_node(of->file->f_path.dentry); > - struct kernfs_open_node *on = kn->attr.open; > + struct kernfs_open_node *on = kernfs_deref_on_raw(kn);
and here.
> @@ -922,13 +950,13 @@ void kernfs_notify(struct kernfs_node *kn) > return; > > /* kick poll immediately */ > - spin_lock_irqsave(&kernfs_open_node_lock, flags); > - on = kn->attr.open; > + rcu_read_lock(); > + on = rcu_dereference(kn->attr.open);
Shouldn't this be kernfs_deref_on() too?
Thanks.
-- tejun
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