char_dev: pin parent kobject
In certain cases (for example when a cdev structure is embedded into
another object whose lifetime is controlled by a separate kobject) it is
beneficial to tie lifetime of another object to the lifetime of
character device so that related object is not freed until after
char_dev object is freed.
To achieve this let's pin kobject's parent when doing cdev_add() and
unpin when last reference to cdev structure is being released.
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/char_dev.c b/fs/char_dev.c
index 3f152b9..afc2bb6 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -471,9 +471,19 @@
*/
int cdev_add(struct cdev *p, dev_t dev, unsigned count)
{
+ int error;
+
p->dev = dev;
p->count = count;
- return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
+
+ error = kobj_map(cdev_map, dev, count, NULL,
+ exact_match, exact_lock, p);
+ if (error)
+ return error;
+
+ kobject_get(p->kobj.parent);
+
+ return 0;
}
static void cdev_unmap(dev_t dev, unsigned count)
@@ -498,14 +508,20 @@
static void cdev_default_release(struct kobject *kobj)
{
struct cdev *p = container_of(kobj, struct cdev, kobj);
+ struct kobject *parent = kobj->parent;
+
cdev_purge(p);
+ kobject_put(parent);
}
static void cdev_dynamic_release(struct kobject *kobj)
{
struct cdev *p = container_of(kobj, struct cdev, kobj);
+ struct kobject *parent = kobj->parent;
+
cdev_purge(p);
kfree(p);
+ kobject_put(parent);
}
static struct kobj_type ktype_cdev_default = {
