From: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Date: Sat, 03 May 2003 14:07:41 +1000
This argument applies to all objects. If you reference count
everything which holds a reference to an object, you can infer the
reference count of the object from the sum of reference counts of its
In practice, as you pointed out in an earlier mail (I think sockets
were your example), doing this proves to be extremely painful. And
we're feeling the pain now.
Please ignore the example code I wrote in that email.
Most of it is inconsistent and frankly garbage. :-)
The "->can_unload()" check is actually simpler than we might initially
suspect. Something like ipv6 might check:
if (atomic_read(&inet6_sock_nr) == 0 &&
atomic_read(&inet6_dev_nr) == 0 &&
Now, here is the important part! When this thing returns "1" the
module.c code does this:
call_rcu(&mod->rcu_head, mod->cleanup, NULL);
This makes sure the guy who killed the last object has indeed
left the module code.