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

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Message-ID: <aed988a09cb4347ec7ac1b682c4ee53b7d2a840b.camel@gmail.com>
Date: Mon, 12 Feb 2024 13:10:27 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Nuno Sa <nuno.sa@...log.com>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
 Frank Rowand <frowand.list@...il.com>, Rob Herring <robh+dt@...nel.org>,
 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>
Cc: 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, 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.

Thanks!
- Nuno Sá