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

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Message-ID: <3202c47d-532d-4c74-aff9-992ec1d9cbeb@kernel.dk>
Date: Thu, 20 Nov 2025 07:48:58 -0700
From: Jens Axboe <axboe@...nel.dk>
To: david.laight.linux@...il.com, linux-kernel@...r.kernel.org,
 io-uring@...r.kernel.org
Subject: Re: [PATCH 04/44] io_uring/net: Change some dubious min_t()

On 11/19/25 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);
      |                                        ^
./include/linux/minmax.h:105:19: note: expanded from macro 'min'
  105 | #define min(x, y)       __careful_cmp(min, x, y)
      |                         ^
./include/linux/minmax.h:98:2: note: expanded from macro '__careful_cmp'
   98 |         __careful_cmp_once(op, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
      |         ^
./include/linux/minmax.h:93:2: note: expanded from macro '__careful_cmp_once'
   93 |         BUILD_BUG_ON_MSG(!__types_ok(ux, uy),           \
      |         ^
note: (skipping 2 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
././include/linux/compiler_types.h:590:2: note: expanded from macro '_compiletime_assert'
  590 |         __compiletime_assert(condition, msg, prefix, suffix)
      |         ^
././include/linux/compiler_types.h:583:4: note: expanded from macro '__compiletime_assert'
  583 |                         prefix ## suffix();                             \
      |                         ^
<scratch space>:319:1: note: expanded from here
  319 | __compiletime_assert_2006
      | ^

-- 
Jens Axboe