linux-kernel - Re: [PATCH 1/3] io_uring: Fix use of XArray in __io_uring_files

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Message-ID: <7dd0bd6a-e9e6-e4b8-4343-99681d283306@gmail.com>
Date:   Fri, 9 Oct 2020 15:57:17 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>
Cc:     linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] io_uring: Fix use of XArray in
 __io_uring_files_cancel

On 09/10/2020 15:49, Matthew Wilcox (Oracle) wrote:
> We have to drop the lock during each iteration, so there's no advantage
> to using the advanced API.  Convert this to a standard xa_for_each() loop.

LGTM, but would be better to add

Reported-by: syzbot+27c12725d8ff0bfe1a13@...kaller.appspotmail.com

> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  fs/io_uring.c | 19 +++++--------------
>  1 file changed, 5 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 299c530c66f9..2978cc78538a 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -8665,28 +8665,19 @@ static void io_uring_attempt_task_drop(struct file *file, bool exiting)
>  void __io_uring_files_cancel(struct files_struct *files)
>  {
>  	struct io_uring_task *tctx = current->io_uring;
> -	XA_STATE(xas, &tctx->xa, 0);
> +	struct file *file;
> +	unsigned long index;
>  
>  	/* make sure overflow events are dropped */
>  	tctx->in_idle = true;
>  
> -	do {
> -		struct io_ring_ctx *ctx;
> -		struct file *file;
> -
> -		xas_lock(&xas);
> -		file = xas_next_entry(&xas, ULONG_MAX);
> -		xas_unlock(&xas);
> -
> -		if (!file)
> -			break;
> -
> -		ctx = file->private_data;
> +	xa_for_each(&tctx->xa, index, file) {
> +		struct io_ring_ctx *ctx = file->private_data;
>  
>  		io_uring_cancel_task_requests(ctx, files);
>  		if (files)
>  			io_uring_del_task_file(file);
> -	} while (1);
> +	}
>  }
>  
>  static inline bool io_uring_task_idle(struct io_uring_task *tctx)
> 

-- 
Pavel Begunkov