Re: [PATCH] io_uring: fix bug of wrong BUILD_BUG_ON check

From: Pavel Begunkov <asml.silence@gmail.com>
To: Hao Xu <haoxu@linux.alibaba.com>, Jens Axboe <axboe@kernel.dk>
Cc: io-uring@vger.kernel.org, Joseph Qi <joseph.qi@linux.alibaba.com>
Subject: Re: [PATCH] io_uring: fix bug of wrong BUILD_BUG_ON check
Date: Mon, 6 Sep 2021 16:22:39 +0100	[thread overview]
Message-ID: <f3857fde-7b3d-3d4f-9248-18a5387b8f79@gmail.com> (raw)
In-Reply-To: <20210906151208.206851-1-haoxu@linux.alibaba.com>

On 9/6/21 4:12 PM, Hao Xu wrote:
> Some check should be large than not equal or large than.
> 
> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
> ---
>  fs/io_uring.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 2bde732a1183..3a833037af43 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -10637,13 +10637,13 @@ static int __init io_uring_init(void)
>  		     sizeof(struct io_uring_rsrc_update2));
>  
>  	/* ->buf_index is u16 */
> -	BUILD_BUG_ON(IORING_MAX_REG_BUFFERS >= (1u << 16));
> +	BUILD_BUG_ON(IORING_MAX_REG_BUFFERS > (1u << 16));
>  
>  	/* should fit into one byte */
> -	BUILD_BUG_ON(SQE_VALID_FLAGS >= (1 << 8));
> +	BUILD_BUG_ON(SQE_VALID_FLAGS > (1 << 8));

0xff = 255 is the largest number fitting in u8,
1<<8 = 256.

let SQE_VALID_FLAGS = 256,
(256 > (1<<8)) == (256 > 256) == false,  even though it can't
be represented by u8.


>  	BUILD_BUG_ON(ARRAY_SIZE(io_op_defs) != IORING_OP_LAST);
> -	BUILD_BUG_ON(__REQ_F_LAST_BIT >= 8 * sizeof(int));
> +	BUILD_BUG_ON(__REQ_F_LAST_BIT > 8 * sizeof(int));
>  
>  	req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC |
>  				SLAB_ACCOUNT);
> 

-- 
Pavel Begunkov