Re: [PATCH V2 1/5] block: introduce blk_quiesce_timeout() and blk_unquiesce_timeout()

[jianchao.wang]

Hi ming

On 04/29/2018 11:41 PM, Ming Lei wrote:
>  
> +static void __blk_unquiesce_timeout(struct request_queue *q)
> +{
> +     unsigned long flags;
> +
> +     spin_lock_irqsave(q->queue_lock, flags);
> +     q->timeout_off = false;
> +     spin_unlock_irqrestore(q->queue_lock, flags);
> +}
> +
> +void blk_unquiesce_timeout(struct request_queue *q)
> +{
> +     __blk_unquiesce_timeout(q);
> +     mod_timer(&q->timeout, jiffies + q->rq_timeout);
> +}
> +EXPORT_SYMBOL(blk_unquiesce_timeout);
> +
> +void blk_quiesce_timeout(struct request_queue *q)
> +{
> +     unsigned long flags;
> +
> +     spin_lock_irqsave(q->queue_lock, flags);
> +     q->timeout_off = true;
> +     spin_unlock_irqrestore(q->queue_lock, flags);
> +
> +     del_timer_sync(&q->timeout);
> +     cancel_work_sync(&q->timeout_work);
> +}
> +EXPORT_SYMBOL(blk_quiesce_timeout);
> +
>  /**
>   * blk_sync_queue - cancel any pending callbacks on a queue
>   * @q: the queue
> @@ -408,8 +437,7 @@ EXPORT_SYMBOL(blk_stop_queue);
>   */
>  void blk_sync_queue(struct request_queue *q)
>  {
> -     del_timer_sync(&q->timeout);
> -     cancel_work_sync(&q->timeout_work);
> +     blk_quiesce_timeout(q);
>  
>       if (q->mq_ops) {
>               struct blk_mq_hw_ctx *hctx;
> @@ -421,6 +449,8 @@ void blk_sync_queue(struct request_queue *q)
>       } else {
>               cancel_delayed_work_sync(&q->delay_work);
>       }
> +
> +     __blk_unquiesce_timeout(q);
>  }
>  EXPORT_SYMBOL(blk_sync_queue);
>  
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 0dc9e341c2a7..890dd3b3e3e1 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -901,6 +901,15 @@ static void blk_mq_timeout_work(struct work_struct *work)
>       };
>       struct blk_mq_hw_ctx *hctx;
>       int i;
> +     bool timeout_off;
> +     unsigned long flags;
> +
> +     spin_lock_irqsave(q->queue_lock, flags);
> +     timeout_off = q->timeout_off;
> +     spin_unlock_irqrestore(q->queue_lock, flags);
> +
> +     if (timeout_off)
> +             return;

Looks like there is still race as following:

blk_quiesce_timeout                          blk_mq_timeout_work
                                               -> timeout_off = q->timeout_off; 
//still a false
  -> q->timeout_off = true;
  -> del_timer_sync(&q->timeout);
                                               -> mod_timer
  -> cancel_work_sync(&q->timeout_work);


How about this:

Introduce a new request queue flag QUEUE_FLAG_TIMEOUT_QUIESCED

void blk_quiesce_queue_timeout(struct request_queue *q)
{
        unsigned long flags;

        spin_lock_irqsave(q->queue_lock, flags);
        queue_flag_set(QUEUE_FLAG_TIMEOUT_QUIESCED, q);
        spin_unlock_irqrestore(q->queue_lock, flags);

        synchronize_rcu_bh();
        cancel_work_sync(&q->timeout_work);
        /*
         * The timeout work will not be invoked anymore.
         */
        del_timer_sync(&q->timeout);
}

 void blk_set_queue_dying(struct request_queue *q)
 {
        spin_lock_irq(q->queue_lock);
@@ -867,6 +905,9 @@ static void blk_rq_timed_out_timer(struct timer_list *t)
 {
        struct request_queue *q = from_timer(q, t, timeout);
 
+       if (blk_queue_timeout_quiesced(q))
+               return;

        kblockd_schedule_work(&q->timeout_work);
 }

Thanks
Jianchao