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

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

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.

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