Re: [PATCH 1/6] mm/page_owner: extract page_owner_next_eligible() from read loop

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] mm: soft lockup in page_owner_next_eligible() due to missing cond_resched()
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commit 303a10c305ed333982228df86334f12bd6d8a3c2
Author: Zhen Ni <zhen.ni@easystack.cn>

mm/page_owner: extract page_owner_next_eligible() from read loop

This commit extracts the page scanning logic from read_page_owner() into a
dedicated helper, page_owner_next_eligible(). It advances a cursor to the
next eligible page and takes a snapshot of the page_owner record inside the
page_ext RCU window.

> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index fbbda7ba914ba..bafe474f33602 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c

[ ... ]

> @@ -798,37 +795,67 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>  			goto ext_put_continue;
>  
>  		/*
> -		 * Access to page_ext->handle isn't synchronous so we should
> -		 * be careful to access it.
> +		 * Take a snapshot of the page_owner record inside the RCU
> +		 * window, then validate it, so that print_page_owner()
> +		 * reads the checked handle from the same snapshot.
>  		 */
> -		handle = READ_ONCE(page_owner->handle);
> -		if (!handle)
> -			goto ext_put_continue;
> +		scan->pfn = pfn;
> +		scan->page = page;
> +		scan->po_snap = *page_owner;
> +		page_ext_put(page_ext);
>  
> +		if (!scan->po_snap.handle)
> +			continue;

[Severity: High]
Could this cause a soft lockup? By using a continue statement here in
page_owner_next_eligible(), we jump directly to the next loop iteration
(advancing pfn) without executing cond_resched() at the end of the loop
block.

If a large contiguous sequence of allocated pages lacks stack handles
(e.g., if stack depot is exhausted or during early non-tracked allocations),
the kernel could iterate over millions of pages without yielding.

The original implementation used goto ext_put_continue; which correctly
yielded. Does this need to be updated to explicitly yield or use the
goto instead?

> +
> +		return true;
> +
> +ext_put_continue:
> +		page_ext_put(page_ext);
> +		cond_resched();
> +	}

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Sashiko AI review · https://sashiko.dev/#/patchset/20261009112308.240769-1-zhen.ni@easystack.cn?part=1