linux-kernel - Re: [PATCH v3] mm/damon/paddr: fix missing folio

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Date:   Wed, 22 Feb 2023 18:26:53 +0000
From:   SeongJae Park <sj@...nel.org>
To:     unlisted-recipients:; (no To-header on input)
Cc:     SeongJae Park <sj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        wsd_upstream@...iatek.com, casper.li@...iatek.com,
        "andrew . yang" <andrew.yang@...iatek.com>, stable@...r.kernel.org,
        damon@...ts.linux.dev, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v3] mm/damon/paddr: fix missing folio_put()

Hi Andrew,


Thank you for revising this patch!

> From: "andrew.yang" <andrew.yang@...iatek.com>
> 
> damon_get_folio() would always increase folio _refcount and
> folio_isolate_lru() would increase folio _refcount if the folio's lru
> flag is set.
> 
> If an unevictable folio isolated successfully, there will be two more
> _refcount. The one from folio_isolate_lru() will be decreased in
> folio_puback_lru(), but the other one from damon_get_folio() will be
> left behind. This causes a pin page.
> 
> Whatever the case, the _refcount from damon_get_folio() should be
> decreased.
> 
> Signed-off-by: andrew.yang <andrew.yang@...iatek.com>
> Fixes: 57223ac29584 ("mm/damon/paddr: support the pageout scheme")
> Cc: <stable@...r.kernel.org> # 5.16.x

Reviewed-by: SeongJae Park <sj@...nel.org>

This may not cleanly applicable on 6.1.y and 6.2.y.  I would post backports
once this is merged in the mainline, unless others do earlier than me.


Thanks,
SJ

> ---
> v3:
>   add fixes tag and cc stable
> v2:
>   according to David's suggestion
>     1. revise subject
>   according to SeongJae's suggestions
>     1. rebase to mm-unstable tree 
>     2. remove braces for th single statements
> ---
>  mm/damon/paddr.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> index 607bb69e526c..6c655d9b5639 100644
> --- a/mm/damon/paddr.c
> +++ b/mm/damon/paddr.c
> @@ -250,12 +250,11 @@ static unsigned long damon_pa_pageout(struct damon_region *r, struct damos *s)
>  			folio_put(folio);
>  			continue;
>  		}
> -		if (folio_test_unevictable(folio)) {
> +		if (folio_test_unevictable(folio))
>  			folio_putback_lru(folio);
> -		} else {
> +		else
>  			list_add(&folio->lru, &folio_list);
> -			folio_put(folio);
> -		}
> +		folio_put(folio);
>  	}
>  	applied = reclaim_pages(&folio_list);
>  	cond_resched();
> -- 
> 2.18.0
> 
>