[Devel] [PATCH RH7] mm: Fix race between reparenting memcg and list_lru_del()

[Vasily Averin]

I'm going to wait till final patch version will be committed upstream

Kirill,
I belive you will be notified, so please let me know when this happen.

Thank you,
	Vasily Averin

On 12/1/20 1:34 PM, Kirill Tkhai wrote:
> From: Roman Gushchin <guro at fb.com>
> 
> On reparenting struct list_lru_one::nr_items may become
> negative, so all the shrinker bits logic works as not expected.
> 
> This leads to cleared shrinker bit while LRU is not
> actually empty.
> 
> (We will pull description from ms git later, when it's available).
> 
> https://lkml.org/lkml/2020/11/30/1093
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  mm/list_lru.c |    4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 21e12a8364ff..05d517197fbe 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -511,7 +511,6 @@ static void memcg_drain_list_lru_node(struct list_lru *lru, int nid,
>  	struct list_lru_node *nlru = &lru->node[nid];
>  	int dst_idx = memcg_cache_id(dst_memcg);
>  	struct list_lru_one *src, *dst;
> -	bool set;
>  
>  	/*
>  	 * Since list_lru_{add,del} may be called under an IRQ-safe lock,
> @@ -523,9 +522,8 @@ static void memcg_drain_list_lru_node(struct list_lru *lru, int nid,
>  	dst = list_lru_from_memcg_idx(nlru, dst_idx);
>  
>  	list_splice_init(&src->list, &dst->list);
> -	set = (!dst->nr_items && src->nr_items);
>  	dst->nr_items += src->nr_items;
> -	if (set)
> +	if (src->nr_items)
>  		memcg_set_shrinker_bit(dst_memcg, nid, lru_shrinker_id(lru));
>  	src->nr_items = 0;
>  
> 
>