[PATCH v6 2/2] of: dynamic: Synchronize of_changeset_destroy() with the devlink removals

Herve Codina
2024-03-25T15:21:59Z

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@vger.kernel.org
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Saravana Kannan <saravanak@google.com>
Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.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);
}
--
2.44.0