On 10/02, Peter Zijlstra wrote:
>
> From: Oleg Nesterov <o...@redhat.com>
Thanks! I was writing the patch, and I chose almost the same naming ;)
> Signed-off-by: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Oleg Nesterov <o...@redhat.com>
In fact I'd like to add my sob to 1/3 and 3/3 as well.
Paul, to remind, this is only the first step. I am going to send
the following improvements:
1. Add rcu_sync->exlusive. The change is simple, just we
need s/wait_queue_head_t/completion/ in rcu_sync_struct
and a couple of "if (rss->exclusive)" checks in enter/exit.
2. rcu_sync_enter() should return !!need_sync. This can help
in exclusive mode.
3. rcu_sync_struct needs more function pointers (perhaps we
should add a single rcu_sync_struct->ops pointer but this
is minor). See below.
But let me repeat just in case, we should do this later.
And once this series is applied, I'll change percpu_rw_semaphore.
> +struct rcu_sync_struct {
> + int gp_state;
> + int gp_count;
> + wait_queue_head_t gp_wait;
> +
> + int cb_state;
> + struct rcu_head cb_head;
> +
> + void (*sync)(void);
> + void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
Yes, and we also need rcu_sync_struct->barrier(). From the patch I was
working on:
void rcu_sync_wait_for_callback(struct rcu_sync *sync)
{
int cb_state;
BUG_ON(sync->gp_count);
spin_lock_irq(&sync->state_lock);
if (sync->cb_state == CB_REPLAY)
sync->cb_state = CB_PENDING;
cb_state = sync->cb_state;
spin_unlock_irq(&sync->state_lock);
if (cb_state != CB_IDLE) {
rcu_barrier_sched();
BUG_ON(sync->cb_state != CB_IDLE);
}
}
It should be called if you are going to kfree the object.
Perhaps another rcu_sync_struct->state_change(new_state) callback (set
by the user) makes sense too, this can help (for example) to implement
the array of semaphores with a single rcu_sync_struct (freeze_super).
Thanks.
Oleg.
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