[PATCH] cdev: cdev_put oops

While fixing an oops in the st driver in a dirty release path, I
encountered an oops in cdev_put for cdevs allocated using cdev_alloc. If
cdev_del is called when the cdev kobject still has an open user, when the
last cdev_put is called, the cdev_put will call kobject_put, which will end
up ultimately releasing the cdev in cdev_dynamic_release. Patch fixes the
oops by preventing cdev_put from accessing freed memory.

Signed-off-by: Brian King <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/char_dev.c

···
 void cdev_put(struct cdev *p)
 {
 	if (p) {
+		struct module *owner = p->owner;
 		kobject_put(&p->kobj);
-		module_put(p->owner);
+		module_put(owner);
 	}
 }