Re: [PATCH] sbitmap: fix permanent io blocking caused by insufficient wakeup times

[Liu Song]

On 2022/9/17 11:58, Hillf Danton wrote:
> On 17 Sep 2022 10:33:01 +0800 Liu Song <liusong@xxxxxxxxxxxxxxxxx> wrote:
> > @@ -632,10 +633,14 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
> >   		if (ret == wait_cnt) {
> >   			sbq_index_atomic_inc(&sbq->wake_index);
> >   			wake_up_nr(&ws->wait, wake_batch);
> > -			return false;
> > +			if (!nr || *nr <= 0)
> > +				return false;
> >   		}
> >   
> >   		return true;
> > +	} else if (nr && *nr) {
> > +		(*nr)--;
> > +		goto again;
> >   	}
> >   
> >   	return false;
> Hi Song,
>
> See if advancing wake_index can survive your tests.

Hi

Thanks for your suggestion, this problem not only needs to switch a wait 
queue, but also needs to consume "wait_cnt" correctly.


Thanks


> Only for thoughts now.
>
> Hillf
> --- a/lib/sbitmap.c
> +++ b/lib/sbitmap.c
> @@ -611,6 +611,7 @@ static bool __sbq_wake_up(struct sbitmap
>   	if (wait_cnt <= 0) {
>   		int ret;
>   
> +		sbq_index_atomic_inc(&sbq->wake_index);
>   		wake_batch = READ_ONCE(sbq->wake_batch);
>   
>   		/*
> @@ -627,7 +628,6 @@ static bool __sbq_wake_up(struct sbitmap
>   		 */
>   		ret = atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wake_batch);
>   		if (ret == wait_cnt) {
> -			sbq_index_atomic_inc(&sbq->wake_index);
>   			wake_up_nr(&ws->wait, wake_batch);
>   			return false;
>   		}