linux-kernel - Re: [PATCH next] fuse: Fix 'min: signedness error' in fuse_wr

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Message-ID: <20260203010558.GA1648836@ax162>
Date: Mon, 2 Feb 2026 18:05:58 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: david.laight.linux@...il.com, Christian Brauner <brauner@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Miklos Szeredi <miklos@...redi.hu>, Mark Brown <broonie@...nel.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Kees Cook <kees@...nel.org>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Theodore Ts'o <tytso@....edu>, Brian Masney <bmasney@...hat.com>
Subject: Re: [PATCH next] fuse: Fix 'min: signedness error' in fuse_wr_pages()

On Tue, Jan 13, 2026 at 07:22:43PM +0000, david.laight.linux@...il.com wrote:
> From: David Laight <david.laight.linux@...il.com>
> 
> On 32bit systems 'pos' is s64 and everything else is 32bit so the
> first argument to min() is signed - generating a warning.
> On 64bit systems 'len' is 64bit unsigned forcing everything to unsigned.
> 
> Fix by reworking the exprssion to completely avoid 64bit maths on 32bit.
> Use DIV_ROUND_UP() instead of open-coding something equivalent.
> 
> Note that the 32bit 'len' cannot overflow because the syscall interface
> limits read/write (etc) to (INT_MAX - PAGE_SIZE) bytes (even on 64bit).
> 
> Fixes: 0f5bb0cfb0b4 ("fs: use min() or umin() instead of min_t()")

Christian, you took 0f5bb0cfb0b4 in vfs-7.0.misc, could you please apply
this fix? Building this file for 32-bit has been broken for the majority
of the -next cycle (I applied an earlier fix David provided and forgot
to chase it until now).

> Signed-off-by: David Laight <david.laight.linux@...il.com>
> ---
>  fs/fuse/file.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 2595b6b4922b..ff823b0545ed 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -1323,8 +1323,8 @@ 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);
> +	len += pos % PAGE_SIZE;
> +	return min(DIV_ROUND_UP(len, PAGE_SIZE), max_pages);
>  }
>  
>  static ssize_t fuse_perform_write(struct kiocb *iocb, struct iov_iter *ii)
> -- 
> 2.39.5
>