linux-kernel - Re: [PATCH 1/1] io_uring: fix overflowed reqs cancellation

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Message-ID: <eb0da4ac-0deb-1b07-62d7-af7701f2b0d2@gmail.com>
Date:   Wed, 27 May 2020 20:18:23 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] io_uring: fix overflowed reqs cancellation

On 27/05/2020 13:23, Pavel Begunkov wrote:
> Overflowed requests in io_uring_cancel_files() should be shed only of
> inflight and overflowed refs. All other left references are owned by
> someone else. E.g. a submission ref owned by __io_queue_sqe() but not
> yet reached the point of releasing it.
> 
> However, if an overflowed request in io_uring_cancel_files() had extra
> refs, after refcount_sub_and_test(2) check fails, it
> 
> - tries to cancel the req, which is already going away. That's pointless,
> just go for the next lap of inflight waiting.
> 
> - io_put_req() underflowing req->refs of a potentially freed request.e
Probably needs v2, please disregard this for now.

> 
> Fixes: 2ca10259b418 ("io_uring: prune request from overflow list on flush")
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> ---
>  fs/io_uring.c | 16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index de6547e68626..01851a74bb12 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -7483,19 +7483,13 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx,
>  			WRITE_ONCE(ctx->rings->cq_overflow,
>  				atomic_inc_return(&ctx->cached_cq_overflow));
>  
> -			/*
> -			 * Put inflight ref and overflow ref. If that's
> -			 * all we had, then we're done with this request.
> -			 */
> -			if (refcount_sub_and_test(2, &cancel_req->refs)) {
> -				io_free_req(cancel_req);
> -				finish_wait(&ctx->inflight_wait, &wait);
> -				continue;
> -			}
> +			/* Put inflight ref and overflow ref. */
> +			io_double_put_req(cancel_req);
> +		} else {
> +			io_wq_cancel_work(ctx->io_wq, &cancel_req->work);
> +			io_put_req(cancel_req);
>  		}
>  
> -		io_wq_cancel_work(ctx->io_wq, &cancel_req->work);
> -		io_put_req(cancel_req);
>  		schedule();
>  		finish_wait(&ctx->inflight_wait, &wait);
>  	}
> 

-- 
Pavel Begunkov