linux-kernel - [PATCH v5 2/2] of: dynamic: Synchronize of_changeset

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Date: Thu,  7 Mar 2024 12:10:01 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Saravana Kannan <saravanak@...gle.com>
Cc: Lizhi Hou <lizhi.hou@....com>,
	Max Zhen <max.zhen@....com>,
	Sonal Santan <sonal.santan@....com>,
	Stefano Stabellini <stefano.stabellini@...inx.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org,
	Allan Nielsen <allan.nielsen@...rochip.com>,
	Horatiu Vultur <horatiu.vultur@...rochip.com>,
	Steen Hegelund <steen.hegelund@...rochip.com>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Nuno Sa <nuno.sa@...log.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Herve Codina <herve.codina@...tlin.com>,
	stable@...r.kernel.org
Subject: [PATCH v5 2/2] of: dynamic: Synchronize of_changeset_destroy() with the devlink removals

In the following sequence:
  1) of_platform_depopulate()
  2) of_overlay_remove()

During the step 1, devices are destroyed and devlinks are removed.
During the step 2, OF nodes are destroyed but
__of_changeset_entry_destroy() can raise warnings related to missing
of_node_put():
  ERROR: memory leak, expected refcount 1 instead of 2 ...

Indeed, during the devlink removals performed at step 1, the removal
itself releasing the device (and the attached of_node) is done by a job
queued in a workqueue and so, it is done asynchronously with respect to
function calls.
When the warning is present, of_node_put() will be called but wrongly
too late from the workqueue job.

In order to be sure that any ongoing devlink removals are done before
the of_node destruction, synchronize the of_changeset_destroy() with the
devlink removals.

Fixes: 80dd33cf72d1 ("drivers: base: Fix device link removal")
Cc: stable@...r.kernel.org
Signed-off-by: Herve Codina <herve.codina@...tlin.com>
Reviewed-by: Saravana Kannan <saravanak@...gle.com>
Tested-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
Reviewed-by: Nuno Sa <nuno.sa@...log.com>
---
 drivers/of/dynamic.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
index 3bf27052832f..4d57a4e34105 100644
--- a/drivers/of/dynamic.c
+++ b/drivers/of/dynamic.c
@@ -9,6 +9,7 @@
 
 #define pr_fmt(fmt)	"OF: " fmt
 
+#include <linux/device.h>
 #include <linux/of.h>
 #include <linux/spinlock.h>
 #include <linux/slab.h>
@@ -667,6 +668,17 @@ void of_changeset_destroy(struct of_changeset *ocs)
 {
 	struct of_changeset_entry *ce, *cen;
 
+	/*
+	 * When a device is deleted, the device links to/from it are also queued
+	 * for deletion. Until these device links are freed, the devices
+	 * themselves aren't freed. If the device being deleted is due to an
+	 * overlay change, this device might be holding a reference to a device
+	 * node that will be freed. So, wait until all already pending device
+	 * links are deleted before freeing a device node. This ensures we don't
+	 * free any device node that has a non-zero reference count.
+	 */
+	device_link_wait_removal();
+
 	list_for_each_entry_safe_reverse(ce, cen, &ocs->entries, node)
 		__of_changeset_entry_destroy(ce);
 }
-- 
2.43.0