Re: [TOMOYO 05/15](repost) Domain transition handler functions.

Tetsuo Handa
2007-10-03T14:19:33Z

Hello.

Thank you for pointing out.

Peter Zijlstra wrote:
> > Currently, TOMOYO Linux avoids read_lock, on the assumption that
> > (1) First, ptr->next is initialized with NULL.
> > (2) Later, ptr->next is assigned non-NULL address.
> > (3) Assigning to ptr->next is done atomically.
> (4) wmb after asigning ptr->next
> (5) rmb before reading ptr->next
Excuse me, but I didn't understand why (4) and (5) are needed.

append_function() {

down(semaphore_for_write_protect);
...
ptr = head;
while (ptr->next) ptr = ptr->next;
ptr->next = new_entry;
...
up(semaphore_for_write_protect);

}

read_function() {

for (ptr = head; ptr; ptr = ptr->next) {
...
}

}

Are (4) and (5) needed even when (3) is exclusively protected by down() and up() ?

Regards.