Re: [PATCH] io_uring: trigger worker exit when ring is exiting

[Pavel Begunkov <asml.silence@gmail.com>]

On 9/2/21 6:56 PM, Jens Axboe wrote:
> If a task exits normally, then the teardown of async workers happens
> quickly. But if it simply closes the ring fd, then the async teardown
> ends up waiting for workers to timeout if they are sleeping, which can
> then take up to 5 seconds (by default). This isn't a big issue as this
> happens off the workqueue path, but let's be nicer and ensure that we
> exit as quick as possible.

ring = io_uring_init();
...
io_uring_close(&ring); // triggers io_ring_ctx_wait_and_kill()
rint2 = io_uring_init();
...

It looks IO_WQ_BIT_EXIT there will be troublesome.

> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> 
> ---
> 
> diff --git a/fs/io-wq.c b/fs/io-wq.c
> index d80e4a735677..60cd841c6c57 100644
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -1130,7 +1130,17 @@ static bool io_task_work_match(struct callback_head *cb, void *data)
>  
>  void io_wq_exit_start(struct io_wq *wq)
>  {
> +	int node;
> +
>  	set_bit(IO_WQ_BIT_EXIT, &wq->state);
> +
> +	rcu_read_lock();
> +	for_each_node(node) {
> +		struct io_wqe *wqe = wq->wqes[node];
> +
> +		io_wq_for_each_worker(wqe, io_wq_worker_wake, NULL);
> +	}
> +	rcu_read_unlock();
>  }
>  
>  static void io_wq_exit_workers(struct io_wq *wq)
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 2bde732a1183..9936ebaa8180 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -9158,6 +9158,7 @@ static bool io_kill_timeouts(struct io_ring_ctx *ctx, struct task_struct *tsk,
>  
>  static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
>  {
> +	struct io_uring_task *tctx = current->io_uring;
>  	unsigned long index;
>  	struct creds *creds;
>  
> @@ -9175,6 +9176,10 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
>  	/* if we failed setting up the ctx, we might not have any rings */
>  	io_iopoll_try_reap_events(ctx);
>  
> +	/* trigger exit, if it hasn't been done already */
> +	if (tctx->io_wq)
> +		io_wq_exit_start(tctx->io_wq);
> +
>  	INIT_WORK(&ctx->exit_work, io_ring_exit_work);
>  	/*
>  	 * Use system_unbound_wq to avoid spawning tons of event kworkers
> 

-- 
Pavel Begunkov