[PATCH v3 2/2] of: overlay: Synchronize of_overlay_remove() with the devlink removals

[Herve Codina <herve.codina@bootlin.com>]

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_overlay_remove() with the
devlink removals.

Fixes: 80dd33cf72d1 ("drivers: base: Fix device link removal")
Cc: stable@vger.kernel.org
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
---
 drivers/of/overlay.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 2ae7e9d24a64..7a010a62b9d8 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -8,6 +8,7 @@
 
 #define pr_fmt(fmt)	"OF: overlay: " fmt
 
+#include <linux/device.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/of.h>
@@ -853,6 +854,14 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
 {
 	int i;
 
+	/*
+	 * Wait for any ongoing device link removals before removing some of
+	 * nodes. Drop the global lock while waiting
+	 */
+	mutex_unlock(&of_mutex);
+	device_link_wait_removal();
+	mutex_lock(&of_mutex);
+
 	if (ovcs->cset.entries.next)
 		of_changeset_destroy(&ovcs->cset);
 
@@ -862,7 +871,6 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
 		ovcs->id = 0;
 	}
 
-
 	for (i = 0; i < ovcs->count; i++) {
 		of_node_put(ovcs->fragments[i].target);
 		of_node_put(ovcs->fragments[i].overlay);
-- 
2.43.0