[PATCH v5 0/4] of: overlay: kobject & sysfs'ation

The first patch puts the overlays as objects in the sysfs in
/sys/firmware/devicetree/overlays.

The next adds a master overlay enable switch (that once is set to
disabled can't be re-enabled), while the one after that
introduces a number of default per overlay attributes.

The patchset is against linus's tree as of today.

The last patch updates the ABI docs for the sysfs entries.

Changes since v4:
* Rebased against latest mainline.

Changes since v3:
* Used strtobool instead of kstrtoul
* ABI Documentation includes a pointer to the discussion that
requested the sysfs property.

Changes since v2:
* Removed the unittest patch.
* Split the sysfs attribute patch to a global and a per-overlay
  patch.
* Dropped binary attributes using textual kobj_attributes instead.

Changes since v1:
* Maintainer requested changes.
* Documented the sysfs entries
* Per overlay sysfs attributes.

Pantelis Antoniou (4):
  of: overlay: kobjectify overlay objects
  of: overlay: global sysfs enable attribute
  of: overlay: add per overlay sysfs attributes
  Documentation: ABI: /sys/firmware/devicetree/overlays

 .../ABI/testing/sysfs-firmware-devicetree-overlays |  35 +++++
 drivers/of/base.c                                  |   7 +
 drivers/of/of_private.h                            |   9 ++
 drivers/of/overlay.c                               | 146 ++++++++++++++++++++-
 4 files changed, 195 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-firmware-devicetree-overlays

-- 
1.7.12

We are going to need the overlays to appear on sysfs with runtime
global properties (like master enable) so turn them into kobjects.

Signed-off-by: Pantelis Antoniou <redacted>
---
 drivers/of/base.c       |  7 +++++++
 drivers/of/of_private.h |  9 +++++++++
 drivers/of/overlay.c    | 52 +++++++++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 8b5a187..31c0c8f 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c

@@ -192,6 +192,7 @@ int __of_attach_node_sysfs(struct device_node *np)
 void __init of_core_init(void)
 {
 	struct device_node *np;
+	int ret;
 
 	/* Create the kset, and register existing nodes */
 	mutex_lock(&of_mutex);

@@ -208,6 +209,12 @@ void __init of_core_init(void)
 	/* Symlink in /proc as required by userspace ABI */
 	if (of_root)
 		proc_symlink("device-tree", NULL, "/sys/firmware/devicetree/base");
+
+	ret = of_overlay_init();
+	if (ret != 0)
+		pr_warn("of_init: of_overlay_init failed!\n");
+
+	return 0;
 }
 
 static struct property *__of_find_property(const struct device_node *np,

diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 8e882e7..120eb44 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h

@@ -90,4 +90,13 @@ extern void __of_detach_node_sysfs(struct device_node *np);
 #define for_each_transaction_entry_reverse(_oft, _te) \
 	list_for_each_entry_reverse(_te, &(_oft)->te_list, node)
 
+#if defined(CONFIG_OF_OVERLAY)
+extern int of_overlay_init(void);
+#else
+static inline int of_overlay_init(void)
+{
+	return 0;
+}
+#endif
+
 #endif /* _LINUX_OF_PRIVATE_H */

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 24e025f..eeb3ec2 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c

@@ -20,6 +20,7 @@
 #include <linux/slab.h>
 #include <linux/err.h>
 #include <linux/idr.h>
+#include <linux/sysfs.h>
 
 #include "of_private.h"
 

@@ -51,6 +52,7 @@ struct of_overlay {
 	int count;
 	struct of_overlay_info *ovinfo_tab;
 	struct of_changeset cset;
+	struct kobject kobj;
 };
 
 static int of_overlay_apply_one(struct of_overlay *ov,

@@ -325,6 +327,24 @@ static int of_free_overlay_info(struct of_overlay *ov)
 static LIST_HEAD(ov_list);
 static DEFINE_IDR(ov_idr);
 
+static inline struct of_overlay *kobj_to_overlay(struct kobject *kobj)
+{
+	return container_of(kobj, struct of_overlay, kobj);
+}
+
+void of_overlay_release(struct kobject *kobj)
+{
+	struct of_overlay *ov = kobj_to_overlay(kobj);
+
+	kfree(ov);
+}
+
+static struct kobj_type of_overlay_ktype = {
+	.release = of_overlay_release,
+};
+
+static struct kset *ov_kset;
+
 /**
  * of_overlay_create() - Create and apply an overlay
  * @tree:	Device node containing all the overlays

@@ -350,6 +370,9 @@ int of_overlay_create(struct device_node *tree)
 
 	of_changeset_init(&ov->cset);
 
+	/* initialize kobject */
+	kobject_init(&ov->kobj, &of_overlay_ktype);
+
 	mutex_lock(&of_mutex);
 
 	id = idr_alloc(&ov_idr, ov, 0, 0, GFP_KERNEL);

@@ -385,6 +408,14 @@ int of_overlay_create(struct device_node *tree)
 		goto err_revert_overlay;
 	}
 
+	ov->kobj.kset = ov_kset;
+	err = kobject_add(&ov->kobj, NULL, "%d", id);
+	if (err != 0) {
+		pr_err("%s: kobject_add() failed for tree@%s\n",
+				__func__, tree->full_name);
+		goto err_cancel_overlay;
+	}
+
 	/* add to the tail of the overlay list */
 	list_add_tail(&ov->node, &ov_list);
 

@@ -392,6 +423,8 @@ int of_overlay_create(struct device_node *tree)
 
 	return id;
 
+err_cancel_overlay:
+	of_changeset_revert(&ov->cset);
 err_revert_overlay:
 err_abort_trans:
 	of_free_overlay_info(ov);

@@ -512,7 +545,9 @@ int of_overlay_destroy(int id)
 	of_free_overlay_info(ov);
 	idr_remove(&ov_idr, id);
 	of_changeset_destroy(&ov->cset);
-	kfree(ov);
+
+	kobject_del(&ov->kobj);
+	kobject_put(&ov->kobj);
 
 	err = 0;
 

@@ -542,7 +577,8 @@ int of_overlay_destroy_all(void)
 		of_changeset_revert(&ov->cset);
 		of_free_overlay_info(ov);
 		idr_remove(&ov_idr, ov->id);
-		kfree(ov);
+		kobject_del(&ov->kobj);
+		kobject_put(&ov->kobj);
 	}
 
 	mutex_unlock(&of_mutex);

@@ -550,3 +586,15 @@ int of_overlay_destroy_all(void)
 	return 0;
 }
 EXPORT_SYMBOL_GPL(of_overlay_destroy_all);
+
+/* called from of_init() */
+int of_overlay_init(void)
+{
+	int rc;
+
+	ov_kset = kset_create_and_add("overlays", NULL, &of_kset->kobj);
+	if (!ov_kset)
+		return -ENOMEM;
+
+	return 0;
+}

-- 
1.7.12

Documentation ABI entry for overlays sysfs entries.

Signed-off-by: Pantelis Antoniou <redacted>
---
 .../ABI/testing/sysfs-firmware-devicetree-overlays | 35 ++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-firmware-devicetree-overlays

diff --git a/Documentation/ABI/testing/sysfs-firmware-devicetree-overlays b/Documentation/ABI/testing/sysfs-firmware-devicetree-overlays
new file mode 100644
index 0000000..2166051
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-firmware-devicetree-overlays

@@ -0,0 +1,35 @@
+What:		/sys/firmware/devicetree/overlays/
+Date:		March 2015
+Contact:	Pantelis Antoniou <pantelis.antoniou@konsulko.com>
+Description:
+		This directory contains the applied device tree overlays of
+		the running system, as directories of the overlay id.
+
+		enable: The master enable switch, by default is 1, and when
+		        set to 0 it cannot be re-enabled for security reasons.
+
+		The discussion about this switch takes place in:
+		http://comments.gmane.org/gmane.linux.drivers.devicetree/101871
+
+		Kees Cook:
+		"Coming from the perspective of drawing a bright line between
+		kernel and the root user (which tends to start with disabling
+		kernel module loading), I would say that there at least needs
+		to be a high-level one-way "off" switch for the interface so
+		that systems that have this interface can choose to turn it off
+		during initial boot, etc."
+
+What:		/sys/firmware/devicetree/overlays/<id>
+Date:		March 2015
+Contact:	Pantelis Antoniou <pantelis.antoniou@konsulko.com>
+Description:
+		Each directory represents an applied overlay, containing
+		the following attribute files.
+
+		targets: A file containing the list of targets of each overlay
+		         with each line containing a target.
+
+		can_remove: The attribute set to 1 means that the overlay can
+		            be removed, while 0 means that the overlay is being
+			    overlapped therefore removal is prohibited.
+

-- 
1.7.12

The two default overlay attributes are:

* A targets sysfs attribute listing the targets of the installed
overlay. The targets list the path on the kernel's device tree
where each overlay fragment is applied to

* A per overlay can_remove sysfs attribute that reports whether
the overlay can be removed or not due to another overlapping overlay.

Signed-off-by: Pantelis Antoniou <redacted>
---
 drivers/of/overlay.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 62cfb99..cff3c05 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c

@@ -373,8 +373,61 @@ static const struct attribute *overlay_global_attrs[] = {
 	NULL
 };
 
+static ssize_t can_remove_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct of_overlay *ov = kobj_to_overlay(kobj);
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", overlay_removal_is_ok(ov));
+}
+
+static ssize_t targets_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct of_overlay *ov = kobj_to_overlay(kobj);
+	struct of_overlay_info *ovinfo;
+	char *s, *e;
+	ssize_t ret;
+	int i, len;
+
+	s = buf;
+	e = buf + PAGE_SIZE;
+
+	mutex_lock(&of_mutex);
+
+	/* targets */
+	for (i = 0; i < ov->count; i++) {
+		ovinfo = &ov->ovinfo_tab[i];
+
+		len = snprintf(s, e - s, "%s\n",
+				of_node_full_name(ovinfo->target));
+		if (len == 0) {
+			ret = -ENOSPC;
+			goto err;
+		}
+		s += len;
+	}
+
+	/* the buffer is zero terminated */
+	ret = s - buf;
+err:
+	mutex_unlock(&of_mutex);
+	return ret;
+}
+
+static struct kobj_attribute can_remove_attr = __ATTR_RO(can_remove);
+static struct kobj_attribute targets_attr = __ATTR_RO(targets);
+
+static struct attribute *overlay_attrs[] = {
+	&can_remove_attr.attr,
+	&targets_attr.attr,
+	NULL
+};
+
 static struct kobj_type of_overlay_ktype = {
 	.release = of_overlay_release,
+	.sysfs_ops = &kobj_sysfs_ops,	/* default kobj sysfs ops */
+	.default_attrs = overlay_attrs,
 };
 
 static struct kset *ov_kset;

-- 
1.7.12

A throw once master enable switch to protect against any
further overlay applications if the administrator desires so.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>
---
 drivers/of/overlay.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index eeb3ec2..62cfb99 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c

@@ -21,6 +21,7 @@
 #include <linux/err.h>
 #include <linux/idr.h>
 #include <linux/sysfs.h>
+#include <linux/atomic.h>
 
 #include "of_private.h"
 

@@ -55,8 +56,12 @@ struct of_overlay {
 	struct kobject kobj;
 };
 
+/* master enable switch; once set to 0 can't be re-enabled */
+static atomic_t ov_enable = ATOMIC_INIT(1);
+
 static int of_overlay_apply_one(struct of_overlay *ov,
 		struct device_node *target, const struct device_node *overlay);
+static int overlay_removal_is_ok(struct of_overlay *ov);
 
 static int of_overlay_apply_single_property(struct of_overlay *ov,
 		struct device_node *target, struct property *prop)

@@ -339,6 +344,35 @@ void of_overlay_release(struct kobject *kobj)
 	kfree(ov);
 }
 
+static ssize_t enable_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%d\n", atomic_read(&ov_enable));
+}
+
+static ssize_t enable_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	int ret;
+	bool new_enable;
+
+	ret = strtobool(buf, &new_enable);
+	if (ret != 0)
+		return ret;
+	/* if we've disabled it, no going back */
+	if (atomic_read(&ov_enable) == 0)
+		return -EPERM;
+	atomic_set(&ov_enable, (int)new_enable);
+	return count;
+}
+
+static struct kobj_attribute enable_attr = __ATTR_RW(enable);
+
+static const struct attribute *overlay_global_attrs[] = {
+	&enable_attr.attr,
+	NULL
+};
+
 static struct kobj_type of_overlay_ktype = {
 	.release = of_overlay_release,
 };

@@ -360,6 +394,10 @@ int of_overlay_create(struct device_node *tree)
 	struct of_overlay *ov;
 	int err, id;
 
+	/* administratively disabled */
+	if (!atomic_read(&ov_enable))
+		return -EPERM;
+
 	/* allocate the overlay structure */
 	ov = kzalloc(sizeof(*ov), GFP_KERNEL);
 	if (ov == NULL)

@@ -596,5 +634,8 @@ int of_overlay_init(void)
 	if (!ov_kset)
 		return -ENOMEM;
 
-	return 0;
+	rc = sysfs_create_files(&ov_kset->kobj, overlay_global_attrs);
+	WARN(rc, "%s: error adding global attributes\n", __func__);
+
+	return rc;
 }

-- 
1.7.12

On Wed, Sep 16, 2015 at 11:09 AM, Pantelis Antoniou
[off-list ref] wrote:

The two default overlay attributes are:

* A targets sysfs attribute listing the targets of the installed
overlay. The targets list the path on the kernel's device tree
where each overlay fragment is applied to

* A per overlay can_remove sysfs attribute that reports whether
the overlay can be removed or not due to another overlapping overlay.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>
---

How about an answer to my v4 questions?

Rob

Hi Rob,

On Sep 16, 2015, at 19:45 , Rob Herring [off-list ref] wrote:

On Wed, Sep 16, 2015 at 11:09 AM, Pantelis Antoniou
[off-list ref] wrote:

quoted

The two default overlay attributes are:

* A targets sysfs attribute listing the targets of the installed
overlay. The targets list the path on the kernel's device tree
where each overlay fragment is applied to

* A per overlay can_remove sysfs attribute that reports whether
the overlay can be removed or not due to another overlapping overlay.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>
---

How about an answer to my v4 questions?

Q. "What will a user do with this information? Can this just be debugfs?
Don't we already have the targets in the overlay itself? If we are
going to provide some overlay info, shouldn't we provide all of it
(i.e. the FDT). For example, what do we do on a kexec?”

A. The user can easily tell whether an overlay is removable using the can_remove
attribute. This can be used by higher layer to inform users whether it’s safe to
remove an overlay or not (perhaps light up a BUSY led)

The targets attribute can let the user figure out what devices (as evident by the
nodes they point to) are affected by the overlay. This was actually used by me
to figure out the TI LCDC DRM driver use of overlays by looking at the targets
pointing there.

Debugfs is a bad fit since these are per-overlay attributes that a user-space application
can use to present some kind of meaningful information to the user.

Providing the FDT of the overlay is only possible when the overlay origin is indeed a
DT blob, which is not always the case. The overlay API only uses unflattened trees.
The DT blob can be provided only by the caller, which has access to the blob.
To hang the FDT blob to overlay kobj we need to extend the overlay API to 
return the kobj of the overlay (which I intent to do in the near future).

Kexec is really tricky. I purposefully didn’t try to address it since in the
previous discussion with Grant we couldn’t get to an agreed default. It seems it is
a per-platform/per-policy decision, and we lack the users to tell us which is the most
prominent.
We have two ways to handle it: a) Leave the kernel tree as it is, flatten it and
kexec with it. That would remove the overlays but the state of the the devices would persist.
b) Remove the overlays in the proper sequence and kexec with the clean kernel tree. That
would necessitate the re-application of the overlays to get to the same device tree state.

Rob

Regards

— Pantelis

quoted

drivers/of/overlay.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 53 insertions(+)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 62cfb99..cff3c05 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c

@@ -373,8 +373,61 @@ static const struct attribute *overlay_global_attrs[] = {
       NULL

};

+static ssize_t can_remove_show(struct kobject *kobj,
+               struct kobj_attribute *attr, char *buf)
+{
+       struct of_overlay *ov = kobj_to_overlay(kobj);
+
+       return snprintf(buf, PAGE_SIZE, "%d\n", overlay_removal_is_ok(ov));
+}
+
+static ssize_t targets_show(struct kobject *kobj,
+               struct kobj_attribute *attr, char *buf)
+{
+       struct of_overlay *ov = kobj_to_overlay(kobj);
+       struct of_overlay_info *ovinfo;
+       char *s, *e;
+       ssize_t ret;
+       int i, len;
+
+       s = buf;
+       e = buf + PAGE_SIZE;
+
+       mutex_lock(&of_mutex);
+
+       /* targets */
+       for (i = 0; i < ov->count; i++) {
+               ovinfo = &ov->ovinfo_tab[i];
+
+               len = snprintf(s, e - s, "%s\n",
+                               of_node_full_name(ovinfo->target));
+               if (len == 0) {
+                       ret = -ENOSPC;
+                       goto err;
+               }
+               s += len;
+       }
+
+       /* the buffer is zero terminated */
+       ret = s - buf;
+err:
+       mutex_unlock(&of_mutex);
+       return ret;
+}
+
+static struct kobj_attribute can_remove_attr = __ATTR_RO(can_remove);
+static struct kobj_attribute targets_attr = __ATTR_RO(targets);
+
+static struct attribute *overlay_attrs[] = {
+       &can_remove_attr.attr,
+       &targets_attr.attr,
+       NULL
+};
+
static struct kobj_type of_overlay_ktype = {
       .release = of_overlay_release,
+       .sysfs_ops = &kobj_sysfs_ops,   /* default kobj sysfs ops */
+       .default_attrs = overlay_attrs,
};

static struct kset *ov_kset;
--
1.7.12

On Wed, Sep 16, 2015 at 07:09:08PM +0300, Pantelis Antoniou wrote:

NULL for the parent?  Really?  Where does that cause this kobject to
show up in the sysfs tree?

Two drops of the reference?

Again, why 2?

thanks,

greg k-h

On Wed, Sep 16, 2015 at 07:09:10PM +0300, Pantelis Antoniou wrote:

Multiple values per sysfs file?  Not ok, this is not going to work,
sorry, please fix.

greg k-h

Hi Greg,

On Oct 4, 2015, at 22:22 , Greg Kroah-Hartman [off-list ref] wrote:

On Wed, Sep 16, 2015 at 07:09:08PM +0300, Pantelis Antoniou wrote:

quoted

We are going to need the overlays to appear on sysfs with runtime
global properties (like master enable) so turn them into kobjects.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>
---
drivers/of/base.c       |  7 +++++++
drivers/of/of_private.h |  9 +++++++++
drivers/of/overlay.c    | 52 +++++++++++++++++++++++++++++++++++++++++++++++--
3 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 8b5a187..31c0c8f 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c

@@ -192,6 +192,7 @@ int __of_attach_node_sysfs(struct device_node *np)

void __init of_core_init(void)
{
	struct device_node *np;
+	int ret;

	/* Create the kset, and register existing nodes */
	mutex_lock(&of_mutex);

@@ -208,6 +209,12 @@ void __init of_core_init(void)

	/* Symlink in /proc as required by userspace ABI */
	if (of_root)
		proc_symlink("device-tree", NULL, "/sys/firmware/devicetree/base");
+
+	ret = of_overlay_init();
+	if (ret != 0)
+		pr_warn("of_init: of_overlay_init failed!\n");
+
+	return 0;
}

static struct property *__of_find_property(const struct device_node *np,

diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 8e882e7..120eb44 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h

@@ -90,4 +90,13 @@ extern void __of_detach_node_sysfs(struct device_node *np);

#define for_each_transaction_entry_reverse(_oft, _te) \
	list_for_each_entry_reverse(_te, &(_oft)->te_list, node)

+#if defined(CONFIG_OF_OVERLAY)
+extern int of_overlay_init(void);
+#else
+static inline int of_overlay_init(void)
+{
+	return 0;
+}
+#endif
+
#endif /* _LINUX_OF_PRIVATE_H */

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 24e025f..eeb3ec2 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c

@@ -20,6 +20,7 @@

#include <linux/slab.h>
#include <linux/err.h>
#include <linux/idr.h>
+#include <linux/sysfs.h>

#include "of_private.h"

@@ -51,6 +52,7 @@ struct of_overlay {

	int count;
	struct of_overlay_info *ovinfo_tab;
	struct of_changeset cset;
+	struct kobject kobj;
};

static int of_overlay_apply_one(struct of_overlay *ov,

@@ -325,6 +327,24 @@ static int of_free_overlay_info(struct of_overlay *ov)

static LIST_HEAD(ov_list);
static DEFINE_IDR(ov_idr);

+static inline struct of_overlay *kobj_to_overlay(struct kobject *kobj)
+{
+	return container_of(kobj, struct of_overlay, kobj);
+}
+
+void of_overlay_release(struct kobject *kobj)
+{
+	struct of_overlay *ov = kobj_to_overlay(kobj);
+
+	kfree(ov);
+}
+
+static struct kobj_type of_overlay_ktype = {
+	.release = of_overlay_release,
+};
+
+static struct kset *ov_kset;
+
/**
 * of_overlay_create() - Create and apply an overlay
 * @tree:	Device node containing all the overlays

@@ -350,6 +370,9 @@ int of_overlay_create(struct device_node *tree)

	of_changeset_init(&ov->cset);

+	/* initialize kobject */
+	kobject_init(&ov->kobj, &of_overlay_ktype);
+
	mutex_lock(&of_mutex);

	id = idr_alloc(&ov_idr, ov, 0, 0, GFP_KERNEL);

@@ -385,6 +408,14 @@ int of_overlay_create(struct device_node *tree)

		goto err_revert_overlay;
	}

+	ov->kobj.kset = ov_kset;
+	err = kobject_add(&ov->kobj, NULL, "%d", id);

NULL for the parent?  Really?  Where does that cause this kobject to
show up in the sysfs tree?

It shows up in the root of it’s kset, i.e. /sys/firmware/devicetree/overlays

It’s a common idiom in the kernel as evident by:

$ grep 'kobject_add([^,]*,[^,]NULL' drivers/ -r
drivers/of/base.c:		rc = kobject_add(&np->kobj, NULL, "%s",
drivers/firmware/memmap.c:	if (kobject_add(&entry->kobj, NULL, "%d", map_entries_nr++))
drivers/firmware/efi/runtime-map.c:	ret = kobject_add(&entry->kobj, NULL, "%d", nr);

quoted

@@ -512,7 +545,9 @@ int of_overlay_destroy(int id)

	of_free_overlay_info(ov);
	idr_remove(&ov_idr, id);
	of_changeset_destroy(&ov->cset);
-	kfree(ov);
+
+	kobject_del(&ov->kobj);
+	kobject_put(&ov->kobj);

Two drops of the reference?

There’s a single drop. Only kobject_put drops the reference. But you’re right,
the kobject_del is not required; it’s performed implicitly by the kobj_cleanup()
method.

Fixing in the new patch.

void of_overlay_release(struct kobject *kobj)
{
        struct of_overlay *ov = kobj_to_overlay(kobj);

        of_node_put(ov->target_root);
        kfree(ov->indirect_id);
        kfree(ov);
}

quoted

	err = 0;

@@ -542,7 +577,8 @@ int of_overlay_destroy_all(void)

		of_changeset_revert(&ov->cset);
		of_free_overlay_info(ov);
		idr_remove(&ov_idr, ov->id);
-		kfree(ov);
+		kobject_del(&ov->kobj);
+		kobject_put(&ov->kobj);

Again, why 2?

thanks,

greg k-h

Regards

— Pantelis