Re: fs/xfs/xfs_buf.c:1534 xfs_buf_submit_bio() warn: unsigned '_x' is never less than zero.

From: David Laight <david.laight.linux@gmail.com>
To: Alexandre Ghiti <alex@ghiti.fr>
Cc: Christoph Hellwig <hch@lst.de>, kernel test robot <lkp@intel.com>,
	oe-kbuild-all@lists.linux.dev, linux-kernel@vger.kernel.org,
	Carlos Maiolino <cem@kernel.org>,
	"Darrick J. Wong" <djwong@kernel.org>,
	linux-riscv@lists.infradead.org
Subject: Re: fs/xfs/xfs_buf.c:1534 xfs_buf_submit_bio() warn: unsigned '_x' is never less than zero.
Date: Tue, 18 Feb 2025 19:53:43 +0000	[thread overview]
Message-ID: <20250218195343.10fa6eb9@pumpkin> (raw)
In-Reply-To: <a14347d2-6189-49bc-a1cc-e5959e76e6c2@ghiti.fr>

On Mon, 17 Feb 2025 13:06:49 +0100
Alexandre Ghiti <alex@ghiti.fr> wrote:

> Hi Christoph,
> 
> On 17/02/2025 10:24, Christoph Hellwig wrote:
> > On Mon, Feb 17, 2025 at 01:53:08PM +0800, kernel test robot wrote:  
> >> New smatch warnings:
> >> fs/xfs/xfs_buf.c:1534 xfs_buf_submit_bio() warn: unsigned '_x' is never less than zero.  
> > Looks like this is an issue in the riscv virt_to_page implementation
> > which also shows up in various other places.  Any chance this could get
> > fixed in the riscv code?  
> 
> 
> To me, the only test that could give rise to this warning is the last 
> part of:
> 
> #define is_linear_mapping(x) \
>          ((x) >= PAGE_OFFSET && (!IS_ENABLED(CONFIG_64BIT) || (x) < PAGE_OFFSET + KERN_VIRT_SIZE))
> 
> But given that the config is a 32-bit config, it should not be evaluated 
> at all.
> 
> Could that be a false-positive and then an issue in smatch?

It's not managing to try to build when:
#define PAGE_OFFSET		_AC(CONFIG_PAGE_OFFSET, UL)
is zero?

I think that is supposed to be (near) the user-kernel boundary.
So probably 0x80000000 or 0xc0000000.
(or 0xe0000000 for some old sparc32)

	David

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