linux-kernel - Re: [PATCH] mm: workingset: Simplify lockdep check in update

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Message-ID: <bmzzod73cuumphqg6nyhegogc6wciyw7oewydljexni7tgdcni@32hathqdj7qo>
Date: Mon, 21 Apr 2025 18:39:53 +0100
From: Pedro Falcato <pfalcato@...e.de>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH] mm: workingset: Simplify lockdep check in update_node

On Mon, Apr 21, 2025 at 06:16:28PM +0100, Pedro Falcato wrote:
> container_of(node->array, ..., i_pages) just to access i_pages again
> is an incredibly roundabout way of accessing node->array itself.
> Simplify it.
> 
> Signed-off-by: Pedro Falcato <pfalcato@...e.de>
> ---
>  mm/workingset.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/mm/workingset.c b/mm/workingset.c
> index 4841ae8af41113797378846f08336cd7c5757bd5..6e7f4cb1b9a7807e9288955f180a5b6cffab1a40 100644
> --- a/mm/workingset.c
> +++ b/mm/workingset.c
> @@ -612,7 +612,6 @@ struct list_lru shadow_nodes;
>  
>  void workingset_update_node(struct xa_node *node)
>  {
> -	struct address_space *mapping;
>  	struct page *page = virt_to_page(node);
>  
>  	/*
> @@ -623,8 +622,7 @@ void workingset_update_node(struct xa_node *node)
>  	 * already where they should be. The list_empty() test is safe
>  	 * as node->private_list is protected by the i_pages lock.
>  	 */
> -	mapping = container_of(node->array, struct address_space, i_pages);
> -	lockdep_assert_held(&mapping->i_pages.xa_lock);
> +	lockdep_assert_held(&node->array->xa_lock);
>  
>  	if (node->count && node->count == node->nr_values) {
>  		if (list_empty(&node->private_list)) {
> 

Actually, not sure if this is wanted given the original code is a little more
explicit on what the lock is. +CC the original author

If people think this is worse, just drop the patch, I don't really care - was just
checking out the function for other purposes and found this bit a little confusing.

-- 
Pedro