On Sat, Feb 9, 2013 at 3:42 PM, Michel Lespinasse <wal...@google.com> wrote:
> On Fri, Feb 8, 2013 at 11:30 PM, Hillf Danton <dhi...@gmail.com> wrote:
>> On Sat, Feb 9, 2013 at 10:45 AM, Michel Lespinasse <wal...@google.com> wrote:
>>> + if (waiter->type != RWSEM_WAITING_FOR_WRITE) {
>>> + list_del(&waiter->list);
>>> +
>>> + /* Set RWSEM_WAITING_BIAS before waking the last
>>> reader
>>> + * so we know there will be a remaining active
>>> locker.
>>> + */
>>> + if (!(--readers) && !list_empty(&sem->wait_list))
>>> + rwsem_atomic_add(RWSEM_WAITING_BIAS, sem);
>>> +
>>> + tsk = waiter->task;
>>> + smp_mb();
>>
>> For what with mb?
>
> This is the same mb that used to be before the readers_only label
> before this change.
> The intention is that the write to waiter->task must be the last
> access to waiter - after that, the reader is granted the lock so it
> could do anything, including deallocating the waiter structure as it
> gets out of rwsem_down_read_failed() and possibly deallocating the
> task structure if it exits
>
Perhaps the waiting process needs to see if no more wait needed,
/* wait to be given the lock */
for (;;) {
if (!waiter.task)
break;
schedule();
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
}
and another mb do exist at the beginning of try_to_wake_up().
And I want to change
+ /* Block until there are no active lockers. */
+ do {
+ schedule();
+ set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+ } while (sem->count & RWSEM_ACTIVE_MASK);
to
/* Block until there are no active lockers. */
while (sem->count & RWSEM_ACTIVE_MASK) {
schedule();
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
}
for sure that we have to wait.
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