Re: [PATCH] io_uring: fix io_sq_thread_stop running in front of io_sq_thread

[Jens Axboe <axboe@kernel.dk>]

On 7/5/19 12:12 AM, Jackie Liu wrote:
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 4ef62a4..4bbecbb 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -231,6 +231,7 @@ struct io_ring_ctx {
>   	struct task_struct	*sqo_thread;	/* if using sq thread polling */
>   	struct mm_struct	*sqo_mm;
>   	wait_queue_head_t	sqo_wait;
> +	bool			sqo_thread_started;
>   
>   	struct {
>   		/* CQ ring */
> @@ -2009,6 +2010,8 @@ static int io_sq_thread(void *data)
>   	unsigned inflight;
>   	unsigned long timeout;
>   
> +	ctx->sqo_thread_started = true;
> +
>   	old_fs = get_fs();
>   	set_fs(USER_DS);
>   
> @@ -2243,6 +2246,8 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
>   static void io_sq_thread_stop(struct io_ring_ctx *ctx)
>   {
>   	if (ctx->sqo_thread) {
> +		while (!ctx->sqo_thread_started)
> +			schedule();
>   		/*
>   		 * The park is a bit of a work-around, without it we get
>   		 * warning spews on shutdown with SQPOLL set and affinity
> 

Probably want to make that an unsigned long, and then use
set_bit/test_bit for this to avoid funky memory ordering issues.

-- 
Jens Axboe