[PATCH 1/1] io_uring: fix overflowed reqs cancellation

[PATCH 1/1] io_uring: fix overflowed reqs cancellation

[Pavel Begunkov]

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.

Fixes: 2ca10259b418 ("io_uring: prune request from overflow list on flush")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.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);
 	}
-- 
2.24.0

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

[Pavel Begunkov]

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@gmail.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