linux-kernel - Re: [BUG] -next lockdep invalid wait context

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Message-ID: <20241108171257.i0EpS9m3@linutronix.de>
Date: Fri, 8 Nov 2024 18:12:57 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Tejun Heo <tj@...nel.org>
Cc: Boqun Feng <boqun.feng@...il.com>, Hillf Danton <hdanton@...a.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Marco Elver <elver@...gle.com>, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org, tglx@...utronix.de,
	syzbot <syzbot+6ea37e2e6ffccf41a7e6@...kaller.appspotmail.com>
Subject: Re: [BUG] -next lockdep invalid wait context

On 2024-11-08 07:02:24 [-1000], Tejun Heo wrote:
> Hello,
Hi,

> > @@ -223,12 +226,11 @@ int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
> >  int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from,
> >  			  char *buf, size_t buflen)
> >  {
> > -	unsigned long flags;
> >  	int ret;
> >  
> > -	read_lock_irqsave(&kernfs_rename_lock, flags);
> > +	rcu_read_lock();
> >  	ret = kernfs_path_from_node_locked(to, from, buf, buflen);
> > -	read_unlock_irqrestore(&kernfs_rename_lock, flags);
> > +	rcu_read_unlock();
> >  	return ret;
> >  }
> 
> The _locked suffix looks awkward afterwards. Given that there's no
> restriction on how the function is called anymore, maybe we can just
> collapse _locked bodies into the callers?

Sure.

> ...
> > diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
> > index 87c79d076d6d7..733d89de40542 100644
> > --- a/include/linux/kernfs.h
> > +++ b/include/linux/kernfs.h
> > @@ -199,8 +199,8 @@ struct kernfs_node {
> >  	 * never moved to a different parent, it is safe to access the
> >  	 * parent directly.
> >  	 */
> > -	struct kernfs_node	*parent;
> > -	const char		*name;
> > +	struct kernfs_node	__rcu *parent;
> > +	const char		__rcu *name;
> 
> ->parent doesn't have to be converted to RCU. As long as the node is
> accessible, the parent is guaranteed to be pinned and unchanged. We only
> need to RCUfy ->name.

I was uncertain about parent. But in that case, let me keep parent as-is
and just do name.
Thanks.

> Thanks.
> 

Sebastian