[PATCH 3/3] of: overlay: do not free changeset when of_overlay_apply returns error

[frowand.list@xxxxxxxxx]

From: Frank Rowand <frank.rowand@xxxxxxxx>

New unittests for overlay notifiers reveal a memory leak in
of_overlay_apply() when a notifier returns an error for action
OF_OVERLAY_POST_APPLY.  The pr_err() message is:

   OF: ERROR: memory leak, expected refcount 1 instead of 3,
   of_node_get()/of_node_put() unbalanced - destroy cset entry: attach
   overlay node /testcase-data/overlay-node/test-bus/test-unittest17

Change the error path to no longer call free_overlay_changeset(),
and document that the caller of of_overlay_fdt_apply() may choose
to remove the overlay.

Update the unittest that triggered the error to expect the changed
return values and to call of_overlay_remove().

Signed-off-by: Frank Rowand <frank.rowand@xxxxxxxx>
---

===

Output of the new overlay notifier unittests, as filtered by
scripts/dtc/of_unittest_expect:

   ### dt-test ### pass of_unittest_overlay_notify():2825
ok OF: overlay: overlay changeset pre-apply notifier error -16, target: /testcase-data/overlay-node/test-bus
   ### dt-test ### pass of_unittest_overlay_notify():2846
   ### dt-test ### pass of_unittest_overlay_notify():2851
ok OF: overlay: overlay changeset post-apply notifier error -17, target: /testcase-data/overlay-node/test-bus
   ### dt-test ### pass of_unittest_overlay_notify():2857
   ### dt-test ### pass of_unittest_overlay_notify():2862
   ### dt-test ### pass of_unittest_overlay_notify():2866
   ### dt-test ### pass of_unittest_overlay_notify():2872
   ### dt-test ### pass of_unittest_overlay_notify():2875
ok OF: overlay: overlay changeset pre-remove notifier error -18, target: /testcase-data/overlay-node/test-bus
   ### dt-test ### pass of_unittest_overlay_notify():2886
   ### dt-test ### pass of_unittest_overlay_notify():2894
   ### dt-test ### pass of_unittest_overlay_notify():2898
   ### dt-test ### pass of_unittest_overlay_notify():2901
ok OF: overlay: overlay changeset post-remove notifier error -19, target: /testcase-data/overlay-node/test-bus
   ### dt-test ### pass of_unittest_overlay_notify():2908
   ### dt-test ### pass of_unittest_overlay_notify():2915
   ### dt-test ### pass of_unittest_overlay_notify():2920
   ### dt-test ### pass of_unittest_overlay_notify():2932


 drivers/of/overlay.c  | 29 ++++++++++++++++++++++++++---
 drivers/of/unittest.c | 10 ++++++++--
 2 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 48c240b06d3b..4c1ac36216b8 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -954,6 +954,25 @@ static int of_overlay_apply(struct overlay_changeset *ovcs)
 	return ret;
 }
 
+/*
+ * of_overlay_fdt_apply() - Create and apply an overlay changeset
+ * @overlay_fdt:	pointer to overlay FDT
+ * @overlay_fdt_size:	number of bytes in @overlay_fdt
+ * @ret_ovcs_id:	pointer for returning created changeset id
+ *
+ * Creates and applies an overlay changeset.
+ *
+ * See of_overlay_apply() for important behavior information.
+ *
+ * Return: 0 on success, or a negative error number.  *@ret_ovcs_id is set to
+ * the value of overlay changeset id, which can be passed to of_overlay_remove()
+ * to remove the overlay.
+ *
+ * On error return, the changeset may be partially applied.  This is especially
+ * likely if an OF_OVERLAY_POST_APPLY notifier returns an error.  In this case
+ * the caller should call of_overlay_remove() with the value in *@ret_ovcs_id.
+ */
+
 int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
 			 int *ret_ovcs_id)
 {
@@ -1021,15 +1040,19 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
 	ovcs->overlay_mem = overlay_mem;
 
 	ret = of_overlay_apply(ovcs);
-	if (ret < 0)
-		goto err_free_ovcs;
+	/*
+	 * If of_overlay_apply() error, calling free_overlay_changeset() may
+	 * result in a memory leak if the apply partly succeeded, so do NOT
+	 * goto err_free_ovcs.  Instead, the caller of of_overlay_fdt_apply()
+	 * can call of_overlay_remove();
+	 */
 
 	mutex_unlock(&of_mutex);
 	of_overlay_mutex_unlock();
 
 	*ret_ovcs_id = ovcs->id;
 
-	return 0;
+	return ret;
 
 err_free_ovcs:
 	free_overlay_changeset(ovcs);
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index e28c3df2c4c2..dff55ae09d97 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -2848,7 +2848,7 @@ static void __init of_unittest_overlay_notify(void)
 
 	EXPECT_END(KERN_INFO, "OF: overlay: overlay changeset pre-apply notifier error -16, target: /testcase-data/overlay-node/test-bus");
 
-	unittest(!ovcs_id, "ovcs_id created for overlay_16\n");
+	unittest(ovcs_id, "ovcs_id not created for overlay_16\n");
 
 	/* ---  overlay 17  --- */
 
@@ -2859,7 +2859,13 @@ static void __init of_unittest_overlay_notify(void)
 
 	EXPECT_END(KERN_INFO, "OF: overlay: overlay changeset post-apply notifier error -17, target: /testcase-data/overlay-node/test-bus");
 
-	unittest(!ovcs_id, "ovcs_id created for overlay_17\n");
+	unittest(ovcs_id, "ovcs_id not created for overlay_17\n");
+
+	if (ovcs_id) {
+		ret = of_overlay_remove(&ovcs_id);
+		unittest(!ret,
+			"overlay_17 of_overlay_remove(), ret = %d\n", ret);
+	}
 
 	/* ---  overlay 18  --- */
 
-- 
Frank Rowand <frank.rowand@xxxxxxxx>