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 16:01:15 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Rob Herring <robh@...nel.org>, 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 Tue, 2024-02-13 at 08:51 -0600, Rob Herring wrote:
> 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.
> 

Yeah, I did asked him but I guess he never had the time for it... Saravana,
could you please give some feedback on this? I think the most sensible part is
on the devlink side but I assume this is not going to be merged without an ack
from a DT maintainer...

- Nuno Sá