Re: [PATCH 2/2] io_uring: don't hold uring_lock when calling io_run_task_work*

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

On 03/02/2021 14:57, Hao Xu wrote:
> This is caused by calling io_run_task_work_sig() to do work under
> uring_lock while the caller io_sqe_files_unregister() already held
> uring_lock.
> we need to check if uring_lock is held by us when doing unlock around
> io_run_task_work_sig() since there are code paths down to that place
> without uring_lock held.

1. we don't want to allow parallel io_sqe_files_unregister()s
happening, it's synchronised by uring_lock atm. Otherwise it's
buggy.

2. probably same with unregister and submit.

> 
> Reported-by: Abaci <abaci@linux.alibaba.com>
> Fixes: 1ffc54220c44 ("io_uring: fix io_sqe_files_unregister() hangs")
> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
> ---
>  fs/io_uring.c | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index efb6d02fea6f..b093977713ee 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -7362,18 +7362,25 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx, bool locked)
>  
>  	/* wait for all refs nodes to complete */
>  	flush_delayed_work(&ctx->file_put_work);
> +	if (locked)
> +		mutex_unlock(&ctx->uring_lock);
>  	do {
>  		ret = wait_for_completion_interruptible(&data->done);
>  		if (!ret)
>  			break;
>  		ret = io_run_task_work_sig();
> -		if (ret < 0) {
> -			percpu_ref_resurrect(&data->refs);
> -			reinit_completion(&data->done);
> -			io_sqe_files_set_node(data, backup_node);
> -			return ret;
> -		}
> +		if (ret < 0)
> +			break;
>  	} while (1);
> +	if (locked)
> +		mutex_lock(&ctx->uring_lock);
> +
> +	if (ret < 0) {
> +		percpu_ref_resurrect(&data->refs);
> +		reinit_completion(&data->done);
> +		io_sqe_files_set_node(data, backup_node);
> +		return ret;
> +	}
>  
>  	__io_sqe_files_unregister(ctx);
>  	nr_tables = DIV_ROUND_UP(ctx->nr_user_files, IORING_MAX_FILES_TABLE);
> 

-- 
Pavel Begunkov