linux-kernel - Re: [PATCH v2 2/2] of: dynamic: flush devlinks workqueue before destroying the changeset

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Date: Tue, 13 Feb 2024 08:51:31 -0600
From: Rob Herring <robh@...nel.org>
To: Nuno Sá <noname.nuno@...il.com>,
	Saravana Kannan <saravanak@...gle.com>
Cc: Nuno Sa <nuno.sa@...log.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Daniel Scally <djrscally@...il.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] of: dynamic: flush devlinks workqueue before
 destroying the changeset

On Mon, Feb 12, 2024 at 01:10:27PM +0100, Nuno Sá wrote:
> On Mon, 2024-02-05 at 13:09 +0100, Nuno Sa wrote:
> > Device links will drop their supplier + consumer refcounts
> > asynchronously. That means that the refcount of the of_node attached to
> > these devices will also be dropped asynchronously and so we cannot
> > guarantee the DT overlay assumption that the of_node refcount must be 1 in
> > __of_changeset_entry_destroy().
> > 
> > Given the above, call the new fwnode_links_flush_queue() helper to flush
> > the devlink workqueue so we can be sure that all links are dropped before
> > doing the proper checks.
> > 
> > Signed-off-by: Nuno Sa <nuno.sa@...log.com>
> > ---
> >  drivers/of/dynamic.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
> > index 3bf27052832f..b7153c72c9c9 100644
> > --- a/drivers/of/dynamic.c
> > +++ b/drivers/of/dynamic.c
> > @@ -14,6 +14,7 @@
> >  #include <linux/slab.h>
> >  #include <linux/string.h>
> >  #include <linux/proc_fs.h>
> > +#include <linux/fwnode.h>
> >  
> >  #include "of_private.h"
> >  
> > @@ -518,6 +519,13 @@ EXPORT_SYMBOL(of_changeset_create_node);
> >  
> >  static void __of_changeset_entry_destroy(struct of_changeset_entry *ce)
> >  {
> > +	/*
> > +	 * device links drop their device references (and hence their of_node
> > +	 * references) asynchronously on a dedicated workqueue. Hence we need
> > +	 * to flush it to make sure everything is done before doing the below
> > +	 * checks.
> > +	 */
> > +	fwnode_links_flush_queue();
> >  	if (ce->action == OF_RECONFIG_ATTACH_NODE &&
> >  	    of_node_check_flag(ce->np, OF_OVERLAY)) {
> >  		if (kref_read(&ce->np->kobj.kref) > 1) {
> > 
> 
> Hi Rob and Frank,
> 
> Any way you could take a look at this and see if you're ok with the change in the
> overlay code? 
> 
> On the devlink side , we already got the ok from Rafael.

Didn't Saravana say he was going to look at this? As of yesterday, he's 
also a DT maintainer so deferring to him.

Rob