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Subject[PATCH] kobject: Make sure the parent does not get released before its children
Date
In the function kobject_cleanup(), kobject_del(kobj) is
called before the kobj->release(). That makes it possible to
release the parent of the kobject before the kobject itself.

To fix that, adding function __kboject_del() that does
everything that kobject_del() does except release the parent
reference. kobject_cleanup() then calls __kobject_del()
instead of kobject_del(), and separately decrements the
reference count of the parent kobject after kobj->release()
has been called.

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: kernel test robot <rong.a.chen@intel.com>
Fixes: 7589238a8cf3 ("Revert "software node: Simplify software_node_release() function"")
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Suggested-by: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
---
lib/kobject.c | 30 ++++++++++++++++++++----------
1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/lib/kobject.c b/lib/kobject.c
index 65fa7bf70c57..32432036bef8 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -599,14 +599,7 @@ int kobject_move(struct kobject *kobj, struct kobject *new_parent)
}
EXPORT_SYMBOL_GPL(kobject_move);

-/**
- * kobject_del() - Unlink kobject from hierarchy.
- * @kobj: object.
- *
- * This is the function that should be called to delete an object
- * successfully added via kobject_add().
- */
-void kobject_del(struct kobject *kobj)
+static void __kobject_del(struct kobject *kobj)
{
struct kernfs_node *sd;
const struct kobj_type *ktype;
@@ -625,9 +618,23 @@ void kobject_del(struct kobject *kobj)

kobj->state_in_sysfs = 0;
kobj_kset_leave(kobj);
- kobject_put(kobj->parent);
kobj->parent = NULL;
}
+
+/**
+ * kobject_del() - Unlink kobject from hierarchy.
+ * @kobj: object.
+ *
+ * This is the function that should be called to delete an object
+ * successfully added via kobject_add().
+ */
+void kobject_del(struct kobject *kobj)
+{
+ struct kobject *parent = kobj->parent;
+
+ __kobject_del(kobj);
+ kobject_put(parent);
+}
EXPORT_SYMBOL(kobject_del);

/**
@@ -663,6 +670,7 @@ EXPORT_SYMBOL(kobject_get_unless_zero);
*/
static void kobject_cleanup(struct kobject *kobj)
{
+ struct kobject *parent = kobj->parent;
struct kobj_type *t = get_ktype(kobj);
const char *name = kobj->name;

@@ -684,7 +692,7 @@ static void kobject_cleanup(struct kobject *kobj)
if (kobj->state_in_sysfs) {
pr_debug("kobject: '%s' (%p): auto cleanup kobject_del\n",
kobject_name(kobj), kobj);
- kobject_del(kobj);
+ __kobject_del(kobj);
}

if (t && t->release) {
@@ -698,6 +706,8 @@ static void kobject_cleanup(struct kobject *kobj)
pr_debug("kobject: '%s': free name\n", name);
kfree_const(name);
}
+
+ kobject_put(parent);
}

#ifdef CONFIG_DEBUG_KOBJECT_RELEASE
--
2.26.2
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