memleak around kobject_init_and_add()

From: Tobin C. Harding
Date: Sat Apr 27 2019 - 04:14:15 EST

(Note at bottom on reasons for 'To' list 'Cc' list)


kobject_init_and_add() seems to be routinely misused. A failed call to this
function requires a call to kobject_put() otherwise we leak memory.

Examples memleaks can be seen in:

fs/xfs/xfs_sysfs.h: xfs_sysfs_init()

Question: Do we fix the misuse or fix the API?

$ git grep kobject_init_and_add | wc -l

Either way, we will have to go through all 117 call sites and check them. I
don't mind fixing them all but I don't want to do it twice because I chose the
wrong option. Reaching out to those more experienced for a suggestion please.

Fix the API

Typically init functions do not require cleanup if they fail, this argument
leads to this patch

diff --git a/lib/kobject.c b/lib/kobject.c
index aa89edcd2b63..62328054bbd0 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -453,6 +453,9 @@ int kobject_init_and_add(struct kobject *kobj, struct kobj_type *ktype,
retval = kobject_add_varg(kobj, parent, fmt, args);

+ if (retval)
+ kobject_put(kobj);
return retval;

Fix all the call sites

Go through all 117 call sites and add kobj_put() in the error path.

This example from mm/slub.c

diff --git a/mm/slub.c b/mm/slub.c
index d30ede89f4a6..84a9d6c06c27 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5756,8 +5756,10 @@ static int sysfs_slab_add(struct kmem_cache *s)

s->kobj.kset = kset;
err = kobject_init_and_add(&s->kobj, &slab_ktype, NULL, "%s", name);
- if (err)
+ if (err) {
+ kobject_put(&s->kobj);
goto out;
+ }

err = sysfs_create_group(&s->kobj, &slab_attr_group);
if (err)


This is a Saturday afternoon 'drinking some wine, hacking on the kernel'
email. Sending it to the lib/kobject.c maintainers for obvious
reasons. CC'd a few extra people who I thought might be interested to
take the weight of Greg and Rafael :)