linux-kernel - Re: mm/vmscan.c:3504 walk_pte_range() error: uninitialized symbol 'dirty'.

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Message-Id: <20250523152705.2ecae09e834c66e1327d6748@linux-foundation.org>
Date: Fri, 23 May 2025 15:27:05 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: oe-kbuild@...ts.linux.dev, Yu Zhao <yuzhao@...gle.com>, lkp@...el.com,
 oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org, Linux Memory
 Management List <linux-mm@...ck.org>
Subject: Re: mm/vmscan.c:3504 walk_pte_range() error: uninitialized symbol
 'dirty'.

On Fri, 23 May 2025 13:47:54 +0300 Dan Carpenter <dan.carpenter@...aro.org> wrote:

> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   088d13246a4672bc03aec664675138e3f5bff68c
> commit: a52dcec56c5b96250f15efbd7de3d3ea6ce863d9 mm/mglru: fix PTE-mapped large folios
> config: sparc-randconfig-r073-20250515 (https://download.01.org/0day-ci/archive/20250515/202505152339.fBOfDPsi-lkp@intel.com/config)
> compiler: sparc64-linux-gcc (GCC) 8.5.0
> 
> smatch warnings:
> mm/vmscan.c:3504 walk_pte_range() error: uninitialized symbol 'dirty'.
> mm/vmscan.c:3595 walk_pmd_range_locked() error: uninitialized symbol 'dirty'.
> mm/vmscan.c:4215 lru_gen_look_around() error: uninitialized symbol 'dirty'.
> 
> ...
>
> bd74fdaea14602 Yu Zhao        2022-09-18  3484  	for (i = pte_index(start), addr = start; addr != end; i++, addr += PAGE_SIZE) {
> bd74fdaea14602 Yu Zhao        2022-09-18  3485  		unsigned long pfn;
> bd74fdaea14602 Yu Zhao        2022-09-18  3486  		struct folio *folio;
> c33c794828f212 Ryan Roberts   2023-06-12  3487  		pte_t ptent = ptep_get(pte + i);
> bd74fdaea14602 Yu Zhao        2022-09-18  3488  
> bd74fdaea14602 Yu Zhao        2022-09-18  3489  		total++;
> bd74fdaea14602 Yu Zhao        2022-09-18  3490  		walk->mm_stats[MM_LEAF_TOTAL]++;
> bd74fdaea14602 Yu Zhao        2022-09-18  3491  
> 1d4832becdc2cd Yu Zhao        2024-10-19  3492  		pfn = get_pte_pfn(ptent, args->vma, addr, pgdat);
> bd74fdaea14602 Yu Zhao        2022-09-18  3493  		if (pfn == -1)
> bd74fdaea14602 Yu Zhao        2022-09-18  3494  			continue;
> bd74fdaea14602 Yu Zhao        2022-09-18  3495  
> 798c0330c2ca07 Yu Zhao        2024-12-30  3496  		folio = get_pfn_folio(pfn, memcg, pgdat);
> bd74fdaea14602 Yu Zhao        2022-09-18  3497  		if (!folio)
> bd74fdaea14602 Yu Zhao        2022-09-18  3498  			continue;
> bd74fdaea14602 Yu Zhao        2022-09-18  3499  
> 1d4832becdc2cd Yu Zhao        2024-10-19  3500  		if (!ptep_clear_young_notify(args->vma, addr, pte + i))
> 1d4832becdc2cd Yu Zhao        2024-10-19  3501  			continue;
> bd74fdaea14602 Yu Zhao        2022-09-18  3502  
> a52dcec56c5b96 Yu Zhao        2024-12-30  3503  		if (last != folio) {
> a52dcec56c5b96 Yu Zhao        2024-12-30 @3504  			walk_update_folio(walk, last, gen, dirty);

Seems to be notabug because last==NULL on the first loop and in this
case walk_update_folio() will immediately return without touching
`dirty'.   But gee, I can't blame smatch from getting fooled by this.

(oh look, mm/ has two walk_pte_range()s)