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

[Hao Xu <haoxu@linux.alibaba.com>]

在 2021/9/7 上午3:15, Pavel Begunkov 写道:
> On 9/6/21 6:03 PM, Hao Xu wrote:
>> 在 2021/9/6 下午11:22, Pavel Begunkov 写道:
>>> 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.
>> Isn't SQE_VALID_FLAGS = 256 a valid value for it?
> 
> SQE_VALID_FLAGS is a "bitwise OR" combination of valid flags, so
> can't be go beyond 0xff
I see, don't know why I mix it with __REQ_F_LAST_BIT in my mind..
> 
>>>
>>>
>>>>        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);
>>>>
>>>
>>
>