linux-kernel - Re: [PATCH] fs: fuse: fix max() of incompatible types

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Message-ID: <CAJnrk1bW+OoiZSFOzO8VAtHjS_Us=-AtuBSZZCvnrdvqK-qqfw@mail.gmail.com>
Date: Tue, 23 Dec 2025 14:58:06 -0800
From: Joanne Koong <joannelkoong@...il.com>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Miklos Szeredi <miklos@...redi.hu>, Christian Brauner <brauner@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	"Darrick J. Wong" <djwong@...nel.org>, Jeff Layton <jlayton@...nel.org>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, david.laight.linux@...il.com
Subject: Re: [PATCH] fs: fuse: fix max() of incompatible types

On Tue, Dec 23, 2025 at 1:54 PM Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> The 'max()' value of a 'long long' and an 'unsigned int' is problematic
> if the former is negative:
>
> In function 'fuse_wr_pages',
>     inlined from 'fuse_perform_write' at fs/fuse/file.c:1347:27:
> include/linux/compiler_types.h:652:45: error: call to '__compiletime_assert_390' declared with attribute error: min(((pos + len - 1) >> 12) - (pos >> 12) + 1, max_pages) signedness error
>   652 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>       |                                             ^
>
> Use a temporary variable to make it clearer what is going on here.
>
> Fixes: 0f5bb0cfb0b4 ("fs: use min() or umin() instead of min_t()")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Hi Arnd,

I believe there was a patch sent last week [1] by David that addresses
this as well.

Thanks,
Joanne

[1] https://lore.kernel.org/linux-fsdevel/20251216141647.13911-1-david.laight.linux@gmail.com/

> ---
>  fs/fuse/file.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 4f71eb5a9bac..d3dec67d73fc 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -1323,8 +1323,10 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
>  static inline unsigned int fuse_wr_pages(loff_t pos, size_t len,
>                                      unsigned int max_pages)
>  {
> -       return min(((pos + len - 1) >> PAGE_SHIFT) - (pos >> PAGE_SHIFT) + 1,
> -                  max_pages);
> +       unsigned int pages = ((pos + len - 1) >> PAGE_SHIFT) -
> +                            (pos >> PAGE_SHIFT) + 1;
> +
> +       return min(pages, max_pages);
>  }
>
>  static ssize_t fuse_perform_write(struct kiocb *iocb, struct iov_iter *ii)
> --
> 2.39.5
>