linux-kernel - Re: [PATCH 04/44] io_uring/net: Change some dubious min

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Message-ID: <312fe285-3915-4108-bc49-3357977d644d@kernel.dk>
Date: Thu, 20 Nov 2025 08:53:56 -0700
From: Jens Axboe <axboe@...nel.dk>
To: David Laight <david.laight.linux@...il.com>
Cc: linux-kernel@...r.kernel.org, io-uring@...r.kernel.org
Subject: Re: [PATCH 04/44] io_uring/net: Change some dubious min_t()

On 11/20/25 8:48 AM, David Laight wrote:
> On Thu, 20 Nov 2025 07:48:58 -0700
> Jens Axboe <axboe@...nel.dk> wrote:
> 
>> On 11/19/25 3:41 PM, david.laight.linux@...il.com wrote:
>>> From: David Laight <david.laight.linux@...il.com>
>>>
>>> Since iov_len is 'unsigned long' it is possible that the cast
>>> to 'int' will change the value of min_t(int, iov[nbufs].iov_len, ret).
>>> Use a plain min() and change the loop bottom to while (ret > 0) so that
>>> the compiler knows 'ret' is always positive.
>>>
>>> Also change min_t(int, sel->val, sr->mshot_total_len) to a simple min()
>>> since sel->val is also long and subject to possible trunctation.
>>>
>>> It might be that other checks stop these being problems, but they are
>>> picked up by some compile-time tests for min_t() truncating values.  
>>
>> Fails with clang-21:
>>
>> io_uring/net.c:855:26: error: call to '__compiletime_assert_2006' declared with 'error' attribute: min(sel->val, sr->mshot_total_len) signedness error
>>   855 |                 sr->mshot_total_len -= min(sel->val, sr->mshot_total_len);
> 
> I'll take a look, I normally use gcc but there must be something
> subtle going on. Actually which architecture? I only tested x86-64.

This is x86-64.

-- 
Jens Axboe