linux-kernel - Re: mm/workingset.c:621 workingset_update_node() warn: unsigned '_x' is never less than zero.

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Message-ID: <ca8bf710-f77a-42b7-92ed-5d6ef9fe44b5@ghiti.fr>
Date: Tue, 18 Feb 2025 05:55:01 +0100
From: Alexandre Ghiti <alex@...ti.fr>
To: Andrew Morton <akpm@...ux-foundation.org>,
 kernel test robot <lkp@...el.com>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>, oe-kbuild-all@...ts.linux.dev,
 linux-kernel@...r.kernel.org,
 Linux Memory Management List <linux-mm@...ck.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 "T.J. Mercier" <tjmercier@...gle.com>, linux-riscv@...ts.infradead.org
Subject: Re: mm/workingset.c:621 workingset_update_node() warn: unsigned '_x'
 is never less than zero.

Hi Andrew,

On 18/02/2025 05:21, Andrew Morton wrote:
> On Sun, 16 Feb 2025 03:56:06 +0800 kernel test robot <lkp@...el.com> wrote:
>
>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>> head:   7ff71e6d923969d933e1ba7e0db857782d36cd19
>> commit: 4715c6a753dccd15fd3a8928168f57e349205bd4 mm: cleanup WORKINGSET_NODES in workingset
>> date:   9 months ago
>> config: riscv-randconfig-r073-20250213 (https://download.01.org/0day-ci/archive/20250216/202502160323.ZLUfooA0-lkp@intel.com/config)
>> compiler: riscv32-linux-gcc (GCC) 14.2.0
>>
>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>> the same patch/commit), kindly add following tags
>> | Reported-by: kernel test robot <lkp@...el.com>
>> | Closes: https://lore.kernel.org/oe-kbuild-all/202502160323.ZLUfooA0-lkp@intel.com/
>>
>> New smatch warnings:
>> mm/workingset.c:621 workingset_update_node() warn: unsigned '_x' is never less than zero.
>> mm/workingset.c:746 shadow_lru_isolate() warn: unsigned '_x' is never less than zero.
>>
>> Old smatch warnings:
>> include/linux/mm.h:1306 virt_to_head_page() warn: unsigned '_x' is never less than zero.
>>
>> vim +/_x +621 mm/workingset.c
>>
>>     617	
>>     618	void workingset_update_node(struct xa_node *node)
>>     619	{
>>     620		struct address_space *mapping;
>>   > 621		struct page *page = virt_to_page(node);
> We're seeing several reports like this.  It looks like the RISC-V
> virt_to_page() (actualy __pa) implementation needs some attention.

Yes, Christoph reported the same warning yesterday, we are discussing it 
since it is probably a false-positive 
https://lore.kernel.org/linux-riscv/Z7PWuSA4jtZnxp5J@rli9-mobl/T/#t.

Thanks,

Alex

>
>
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> linux-riscv@...ts.infradead.org
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