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

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Date: Mon, 05 Feb 2024 13:09:33 +0100
From: Nuno Sa via B4 Relay <devnull+nuno.sa.analog.com@...nel.org>
To: 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: [PATCH v2 2/2] of: dynamic: flush devlinks workqueue before
 destroying the changeset

From: Nuno Sa <nuno.sa@...log.com>

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) {

-- 
2.43.0