linux-kernel - Re: fs/xfs/xfs_buf.c:1534 xfs_buf_submit_bio() warn: unsigned '

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Message-ID: <78ff844a-0fb4-42f6-b54f-4d19e14cfd05@stanley.mountain>
Date: Tue, 18 Feb 2025 17:21:27 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Philip Li <philip.li@...el.com>
Cc: David Laight <david.laight.linux@...il.com>,
	Alexandre Ghiti <alex@...ti.fr>, Christoph Hellwig <hch@....de>,
	kernel test robot <lkp@...el.com>, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org, Carlos Maiolino <cem@...nel.org>,
	"Darrick J. Wong" <djwong@...nel.org>,
	linux-riscv@...ts.infradead.org
Subject: Re: fs/xfs/xfs_buf.c:1534 xfs_buf_submit_bio() warn: unsigned '_x'
 is never less than zero.

On Tue, Feb 18, 2025 at 08:39:21AM +0800, Philip Li wrote:
> + Dan
> 
> Hi Dan,
> 
> On Mon, Feb 17, 2025 at 01:12:03PM +0000, David Laight wrote:
> > On Mon, 17 Feb 2025 13:06:49 +0100
> > Alexandre Ghiti <alex@...ti.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?
> > 
> > Why is smatch even looking.
> > The equivalent check in gcc has been moved to -W2 because of all false positives.

The Smatch check is a bit more sophisticated than the GCC check...
I think if you removed the (!IS_ENABLED(CONFIG_64BIT) condition then
Smatch wouldn't trigger a warning here.  How would I duplicate this
warning?  The "ARCH=riscv make.cross" command does a 64bit build.

Screw it, I can just silence this warning based on that it's a kernel
build and the variable is called "_x".

regards,
dan carpenter