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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