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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 20:15:50 +0100	[thread overview]
Message-ID: <af3ee4c6-86bc-e8b0-227e-a109c75ae12d@gmail.com> (raw)
In-Reply-To: <702b94b7-bd2f-f89c-b835-3345b8fcaa4a@linux.alibaba.com>

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

>>
>>
>>>       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

  reply	other threads:[~2021-09-06 19:17 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-06 15:12 [PATCH] io_uring: fix bug of wrong BUILD_BUG_ON check Hao Xu
2021-09-06 15:22 ` Pavel Begunkov
2021-09-06 17:03   ` Hao Xu
2021-09-06 19:15     ` Pavel Begunkov [this message]
2021-09-07  3:02       ` Hao Xu

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