linux-kernel - Re: [PATCH 06/16] mm/page_alloc: fix freeing static percpu memory

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Date:   Fri, 9 Sep 2022 13:28:40 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     osalvador@...e.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/16] mm/page_alloc: fix freeing static percpu memory

On 09.09.22 11:24, Miaohe Lin wrote:
> The size of struct per_cpu_zonestat can be 0 on !SMP && !NUMA. In that
> case, zone->per_cpu_zonestats will always equal to boot_zonestats. But
> in zone_pcp_reset(), zone->per_cpu_zonestats is freed via free_percpu()
> directly without checking against boot_zonestats first. boot_zonestats
> will be released by free_percpu() unexpectedly.
> 
> Fixes: 28f836b6777b ("mm/page_alloc: split per cpu page lists and zone stats")
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>   mm/page_alloc.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3497919f4ef5..a35ef385d906 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -9510,9 +9510,11 @@ void zone_pcp_reset(struct zone *zone)
>   			drain_zonestat(zone, pzstats);
>   		}
>   		free_percpu(zone->per_cpu_pageset);
> -		free_percpu(zone->per_cpu_zonestats);
>   		zone->per_cpu_pageset = &boot_pageset;
> -		zone->per_cpu_zonestats = &boot_zonestats;
> +		if (zone->per_cpu_zonestats != &boot_zonestats) {
> +			free_percpu(zone->per_cpu_zonestats);
> +			zone->per_cpu_zonestats = &boot_zonestats;
> +		}
>   	}
>   }
>   

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb