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Message-ID: <48a86fa6908a2a7a38a45dc6dbb5574c4a9d7400.camel@gmail.com>
Subject: Re: [PATCH v2 2/2] of: dynamic: flush devlinks workqueue before
 destroying the changeset
From: Nuno =?ISO-8859-1?Q?S=E1?= <noname.nuno@gmail.com>
To: Rob Herring <robh@kernel.org>, Saravana Kannan <saravanak@google.com>
Cc: Nuno Sa <nuno.sa@analog.com>, Greg Kroah-Hartman
 <gregkh@linuxfoundation.org>, "Rafael J. Wysocki" <rafael@kernel.org>,
 Frank Rowand <frowand.list@gmail.com>, Andy Shevchenko
 <andriy.shevchenko@linux.intel.com>, Daniel Scally <djrscally@gmail.com>,
 Heikki Krogerus <heikki.krogerus@linux.intel.com>, Sakari Ailus
 <sakari.ailus@linux.intel.com>, Len Brown <lenb@kernel.org>, 
 linux-acpi@vger.kernel.org, devicetree@vger.kernel.org, 
 linux-kernel@vger.kernel.org
Date: Tue, 13 Feb 2024 16:01:15 +0100
In-Reply-To: <20240213145131.GA1180152-robh@kernel.org>
References: 
	<20240205-fix-device-links-overlays-v2-0-5344f8c79d57@analog.com>
	 <20240205-fix-device-links-overlays-v2-2-5344f8c79d57@analog.com>
	 <aed988a09cb4347ec7ac1b682c4ee53b7d2a840b.camel@gmail.com>
	 <20240213145131.GA1180152-robh@kernel.org>
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On Tue, 2024-02-13 at 08:51 -0600, Rob Herring wrote:
> On Mon, Feb 12, 2024 at 01:10:27PM +0100, Nuno S=C3=A1 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().
> > >=20
> > > Given the above, call the new fwnode_links_flush_queue() helper to fl=
ush
> > > the devlink workqueue so we can be sure that all links are dropped be=
fore
> > > doing the proper checks.
> > >=20
> > > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> > > ---
> > > =C2=A0drivers/of/dynamic.c | 8 ++++++++
> > > =C2=A01 file changed, 8 insertions(+)
> > >=20
> > > 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 @@
> > > =C2=A0#include <linux/slab.h>
> > > =C2=A0#include <linux/string.h>
> > > =C2=A0#include <linux/proc_fs.h>
> > > +#include <linux/fwnode.h>
> > > =C2=A0
> > > =C2=A0#include "of_private.h"
> > > =C2=A0
> > > @@ -518,6 +519,13 @@ EXPORT_SYMBOL(of_changeset_create_node);
> > > =C2=A0
> > > =C2=A0static void __of_changeset_entry_destroy(struct of_changeset_en=
try *ce)
> > > =C2=A0{
> > > +	/*
> > > +	 * 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();
> > > =C2=A0	if (ce->action =3D=3D OF_RECONFIG_ATTACH_NODE &&
> > > =C2=A0	=C2=A0=C2=A0=C2=A0 of_node_check_flag(ce->np, OF_OVERLAY)) {
> > > =C2=A0		if (kref_read(&ce->np->kobj.kref) > 1) {
> > >=20
> >=20
> > Hi Rob and Frank,
> >=20
> > Any way you could take a look at this and see if you're ok with the cha=
nge
> > in the
> > overlay code?=20
> >=20
> > On the devlink side , we already got the ok from Rafael.
>=20
> Didn't Saravana say he was going to look at this? As of yesterday, he's=
=20
> also a DT maintainer so deferring to him.
>=20

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 S=C3=A1