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From: Michal Hocko <mhocko@kernel.org>
To: Wei Yang <richardw.yang@linux.intel.com>
Cc: hannes@cmpxchg.org, vdavydov.dev@gmail.com,
	akpm@linux-foundation.org, kirill.shutemov@linux.intel.com,
	cgroups@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, yang.shi@linux.alibaba.com
Subject: Re: [RFC PATCH] mm: thp: grab the lock before manipulation defer list
Date: Mon, 6 Jan 2020 11:23:45 +0100	[thread overview]
Message-ID: <20200106102345.GE12699@dhcp22.suse.cz> (raw)
In-Reply-To: <20200103143407.1089-1-richardw.yang@linux.intel.com>

On Fri 03-01-20 22:34:07, Wei Yang wrote:
> As all the other places, we grab the lock before manipulate the defer list.
> Current implementation may face a race condition.

Please always make sure to describe the effect of the change. Why a racy
list_empty check matters?

> Fixes: 87eaceb3faa5 ("mm: thp: make deferred split shrinker memcg aware")
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> 
> ---
> I notice the difference during code reading and just confused about the
> difference. No specific test is done since limited knowledge about cgroup.
> 
> Maybe I miss something important?
> ---
>  mm/memcontrol.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index bc01423277c5..62b7ec34ef1a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5368,12 +5368,12 @@ static int mem_cgroup_move_account(struct page *page,
>  	}
>  
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	spin_lock(&from->deferred_split_queue.split_queue_lock);
>  	if (compound && !list_empty(page_deferred_list(page))) {
> -		spin_lock(&from->deferred_split_queue.split_queue_lock);
>  		list_del_init(page_deferred_list(page));
>  		from->deferred_split_queue.split_queue_len--;
> -		spin_unlock(&from->deferred_split_queue.split_queue_lock);
>  	}
> +	spin_unlock(&from->deferred_split_queue.split_queue_lock);
>  #endif
>  	/*
>  	 * It is safe to change page->mem_cgroup here because the page
> @@ -5385,13 +5385,13 @@ static int mem_cgroup_move_account(struct page *page,
>  	page->mem_cgroup = to;
>  
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	spin_lock(&to->deferred_split_queue.split_queue_lock);
>  	if (compound && list_empty(page_deferred_list(page))) {
> -		spin_lock(&to->deferred_split_queue.split_queue_lock);
>  		list_add_tail(page_deferred_list(page),
>  			      &to->deferred_split_queue.split_queue);
>  		to->deferred_split_queue.split_queue_len++;
> -		spin_unlock(&to->deferred_split_queue.split_queue_lock);
>  	}
> +	spin_unlock(&to->deferred_split_queue.split_queue_lock);
>  #endif
>  
>  	spin_unlock_irqrestore(&from->move_lock, flags);
> -- 
> 2.17.1

-- 
Michal Hocko
SUSE Labs

  parent reply	other threads:[~2020-01-06 10:23 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-03 14:34 [RFC PATCH] mm: thp: grab the lock before manipulation defer list Wei Yang
2020-01-03 19:29 ` David Rientjes
2020-01-03 19:29   ` David Rientjes
2020-01-03 23:39   ` Wei Yang
2020-01-04  0:44     ` David Rientjes
2020-01-04  0:44       ` David Rientjes
2020-01-06  1:20       ` Wei Yang
2020-01-06 10:23 ` Michal Hocko [this message]
2020-01-07  1:22   ` Wei Yang
2020-01-07  8:38     ` Michal Hocko
2020-01-08  0:35       ` Wei Yang
2020-01-08  9:40         ` Michal Hocko
2020-01-09  2:03           ` Wei Yang
2020-01-09  8:34             ` Michal Hocko
2020-01-09  2:03           ` Wei Yang
2020-01-09  3:18           ` Wei Yang
2020-01-09  8:36             ` Michal Hocko
2020-01-09  8:52               ` Wei Yang
2020-01-06 16:18 ` Alexander Duyck
2020-01-06 16:18   ` Alexander Duyck
2020-01-07  1:26   ` Wei Yang
2020-01-07  2:07     ` David Rientjes
2020-01-07  2:07       ` David Rientjes
2020-01-07  2:33       ` Wei Yang

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