Re: [PATCH] io-wq: check max_worker limits if a worker transitions bound state

[Hao Xu <haoxu@linux.alibaba.com>]

在 2021/8/30 上午6:19, Jens Axboe 写道:
> For the two places where new workers are created, we diligently check if
> we are allowed to create a new worker. If we're currently at the limit
> of how many workers of a given type we can have, then we don't create
> any new ones.
> 
> If you have a mixed workload with various types of bound and unbounded
> work, then it can happen that a worker finishes one type of work and
> is then transitioned to the other type. For this case, we don't check
> if we are actually allowed to do so. This can cause io-wq to temporarily
> exceed the allowed number of workers for a given type.
> 
> When retrieving work, check that the types match. If they don't, check
> if we are allowed to transition to the other type. If not, then don't
> handle the new work.
> 
> Cc: stable@vger.kernel.org
> Reported-by: Johannes Lundberg <johalun0@gmail.com>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> 
> ---
> 
> diff --git a/fs/io-wq.c b/fs/io-wq.c
> index 4b5fc621ab39..dced22288983 100644
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -424,7 +424,31 @@ static void io_wait_on_hash(struct io_wqe *wqe, unsigned int hash)
>   	spin_unlock(&wq->hash->wait.lock);
>   }
>   
> -static struct io_wq_work *io_get_next_work(struct io_wqe *wqe)
> +/*
> + * We can always run the work if the worker is currently the same type as
> + * the work (eg both are bound, or both are unbound). If they are not the
> + * same, only allow it if incrementing the worker count would be allowed.
> + */
> +static bool io_worker_can_run_work(struct io_worker *worker,
> +				   struct io_wq_work *work)
> +{
> +	struct io_wqe_acct *acct;
> +
> +	if ((worker->flags & IO_WORKER_F_BOUND) &&
> +	    !(work->flags & IO_WQ_WORK_UNBOUND))
> +		return true;
> +	else if (!(worker->flags & IO_WORKER_F_BOUND) &&
> +		 (work->flags & IO_WQ_WORK_UNBOUND))
> +		return true;

How about:
bool a = !(worker->flags & IO_WORKER_F_BOUND);
bool b = !(work->flags & IO_WQ_WORK_UNBOUND);

if (a != b)
     return true;
> +
> +	/* not the same type, check if we'd go over the limit */
> +	acct = io_work_get_acct(worker->wqe, work);
> +	return acct->nr_workers < acct->max_workers;
> +}
> +