Better:
rcu_read_lock();
do {
pgtbl = d->cur_pgtbl;
smp_rmb();
root = d->cur_root;
smp_rmb();
/* d->cur_pgtbl == d->next_pgtbl only during an update. */
} while (pgtbl == d->next_pgtbl);
...
rcu_read_unlock();
And in the writer:
old_pgtbl = d->cur_pgtbl;
/* Point to the new page table, tell readers cur_root is invalid. */
smp_wmb();
d->cur_pgtbl = d->next_pgtbl;
/* Write the root before updating the page table. */
smp_wmb();
d->cur_root = d->next_root;
/* Write cur_root before telling readers it is valid. */
smp_wmb();
d->next_pgtbl = NULL;
/* Drop reference once readers will be done with it. */
call_rcu(page_table_unref, old_pgtbl, rcu);
Paolo
