linux-kernel - Re: [PATCH 30/44] fs: use min() or umin() instead of min

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Message-ID: <20260113183346.18ef7c74@pumpkin>
Date: Tue, 13 Jan 2026 18:33:46 +0000
From: David Laight <david.laight.linux@...il.com>
To: Mark Brown <broonie@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, Alexander Viro
 <viro@...iv.linux.org.uk>, Andreas Dilger <adilger.kernel@...ger.ca>,
 Christian Brauner <brauner@...nel.org>, Kees Cook <kees@...nel.org>, Miklos
 Szeredi <miklos@...redi.hu>, OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
 Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH 30/44] fs: use min() or umin() instead of min_t()

On Tue, 13 Jan 2026 16:56:56 +0000
Mark Brown <broonie@...nel.org> wrote:

> On Wed, Nov 19, 2025 at 10:41:26PM +0000, david.laight.linux@...il.com wrote:
> > From: David Laight <david.laight.linux@...il.com>
> > 
> > min_t(unsigned int, a, b) casts an 'unsigned long' to 'unsigned int'.
> > Use min(a, b) instead as it promotes any 'unsigned int' to 'unsigned long'
> > and so cannot discard significant bits.  
> 
> This breaks an arm imx_v6_v7_defconfig build:

I hadn't tested 32bit when I sent the patch.
It was noticed ages ago and I thought there was a patch (to fuse/file.c) that
changed the code to avoid the 64bit signed maths on 32bit.

	David

> 
> In file included from <command-line>:
> In function 'fuse_wr_pages',
>     inlined from 'fuse_perform_write' at /home/broonie/git/bisect/fs/fuse/file.c:1347:27:
> /home/broonie/git/bisect/include/linux/compiler_types.h:630:45: error: call to '__compiletime_assert_434' declared with attribute error: min(((pos + len - 1) >> 12) - (pos >> 12) + 1, max_pages) signedness error
>   630 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>       |                                             ^
> /home/broonie/git/bisect/include/linux/compiler_types.h:611:25: note: in definition of macro '__compiletime_assert'
>   611 |                         prefix ## suffix();                             \
>       |                         ^~~~~~
> /home/broonie/git/bisect/include/linux/compiler_types.h:630:9: note: in expansion of macro '_compiletime_assert'
>   630 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>       |         ^~~~~~~~~~~~~~~~~~~
> /home/broonie/git/bisect/include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
>    39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>       |                                     ^~~~~~~~~~~~~~~~~~
> /home/broonie/git/bisect/include/linux/minmax.h:93:9: note: in expansion of macro 'BUILD_BUG_ON_MSG'
>    93 |         BUILD_BUG_ON_MSG(!__types_ok(ux, uy),           \
>       |         ^~~~~~~~~~~~~~~~
> /home/broonie/git/bisect/include/linux/minmax.h:98:9: note: in expansion of macro '__careful_cmp_once'
>    98 |         __careful_cmp_once(op, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
>       |         ^~~~~~~~~~~~~~~~~~
> /home/broonie/git/bisect/include/linux/minmax.h:105:25: note: in expansion of macro '__careful_cmp'
>   105 | #define min(x, y)       __careful_cmp(min, x, y)
>       |                         ^~~~~~~~~~~~~
> /home/broonie/git/bisect/fs/fuse/file.c:1326:16: note: in expansion of macro 'min'
>  1326 |         return min(((pos + len - 1) >> PAGE_SHIFT) - (pos >> PAGE_SHIFT) + 1,
>       |                ^~~