linux-kernel - Re: [PATCH 2/3] io_uring: Fix XArray usage in io_uring_add_task

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Date:   Fri, 9 Oct 2020 08:57:55 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Pavel Begunkov <asml.silence@...il.com>
Subject: Re: [PATCH 2/3] io_uring: Fix XArray usage in io_uring_add_task_file

On 10/9/20 6:49 AM, Matthew Wilcox (Oracle) wrote:
> The xas_store() wasn't paired with an xas_nomem() loop, so if it couldn't
> allocate memory using GFP_NOWAIT, it would leak the reference to the file
> descriptor.  Also the node pointed to by the xas could be freed between
> the call to xas_load() under the rcu_read_lock() and the acquisition of
> the xa_lock.
> 
> It's easier to just use the normal xa_load/xa_store interface here.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  fs/io_uring.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 2978cc78538a..bcef6210bf67 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -8586,27 +8586,24 @@ static void io_uring_cancel_task_requests(struct io_ring_ctx *ctx,
>   */
>  static int io_uring_add_task_file(struct file *file)
>  {
> -	if (unlikely(!current->io_uring)) {
> +	struct io_uring_task *cur_uring = current->io_uring;
> +
> +	if (unlikely(!cur_uring)) {
>  		int ret;
>  
>  		ret = io_uring_alloc_task_context(current);
>  		if (unlikely(ret))
>  			return ret;
>  	}

I think this is missing a:

	cur_uring = current->io_uring;

after the successful io_uring_alloc_task(). I'll also rename it to tctx
like what is used in other spots.

Apart from that, series looks good to me, thanks Matthew!

-- 
Jens Axboe