linux-kernel - Re: [PATCH] mm, list_lru: refactor the locking code

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Message-ID: <1c734a50-1ada-40a1-833d-4b94b9849c96@bytedance.com>
Date: Tue, 27 May 2025 10:16:54 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Kairui Song <kasong@...cent.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Johannes Weiner <hannes@...xchg.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Chengming Zhou <zhouchengming@...edance.com>,
 Muchun Song <muchun.song@...ux.dev>, linux-kernel@...r.kernel.org,
 kernel test robot <lkp@...el.com>, Julia Lawall <julia.lawall@...ia.fr>,
 linux-mm@...ck.org
Subject: Re: [PATCH] mm, list_lru: refactor the locking code



On 5/27/25 2:06 AM, Kairui Song wrote:
> From: Kairui Song <kasong@...cent.com>
> 
> Cocci is confused by the try lock then release RCU and return logic
> here. So separate the try lock part out into a standalone helper. The
> code is easier to follow too.
> 
> No feature change, fixes:
> 
> cocci warnings: (new ones prefixed by >>)
>>> mm/list_lru.c:82:3-9: preceding lock on line 77
>>> mm/list_lru.c:82:3-9: preceding lock on line 77
>     mm/list_lru.c:82:3-9: preceding lock on line 75
>     mm/list_lru.c:82:3-9: preceding lock on line 75
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Reported-by: Julia Lawall <julia.lawall@...ia.fr>
> Closes: https://lore.kernel.org/r/202505252043.pbT1tBHJ-lkp@intel.com/
> Signed-off-by: Kairui Song <kasong@...cent.com>
> ---
>   mm/list_lru.c | 34 +++++++++++++++++++---------------
>   1 file changed, 19 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 490473af3122..ec48b5dadf51 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -60,30 +60,34 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
>   	return &lru->node[nid].lru;
>   }
>   
> +static inline bool lock_list_lru(struct list_lru_one *l, bool irq)
> +{
> +	if (irq)
> +		spin_lock_irq(&l->lock);
> +	else
> +		spin_lock(&l->lock);
> +	if (unlikely(READ_ONCE(l->nr_items) == LONG_MIN)) {
> +		if (irq)
> +			spin_unlock_irq(&l->lock);
> +		else
> +			spin_unlock(&l->lock);
> +		return false;
> +	}
> +	return true;
> +}
> +
>   static inline struct list_lru_one *
>   lock_list_lru_of_memcg(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
>   		       bool irq, bool skip_empty)
>   {
>   	struct list_lru_one *l;
> -	long nr_items;
>   
>   	rcu_read_lock();
>   again:
>   	l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
> -	if (likely(l)) {
> -		if (irq)
> -			spin_lock_irq(&l->lock);
> -		else
> -			spin_lock(&l->lock);
> -		nr_items = READ_ONCE(l->nr_items);
> -		if (likely(nr_items != LONG_MIN)) {
> -			rcu_read_unlock();
> -			return l;
> -		}
> -		if (irq)
> -			spin_unlock_irq(&l->lock);
> -		else
> -			spin_unlock(&l->lock);
> +	if (likely(l) && lock_list_lru(l, irq)) {
> +		rcu_read_unlock();
> +		return l;
>   	}
>   	/*
>   	 * Caller may simply bail out if raced with reparenting or

And the code readability has also been improved.

Reviewed-by: Qi Zheng <zhengqi.arch@...edance.com>

Thanks!