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Date:   Wed, 27 Feb 2019 17:21:13 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Qian Cai <cai@....pw>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_ext: fix an imbalance with kmemleak

On Wed, Feb 27, 2019 at 12:15:56PM -0500, Qian Cai wrote:
> After offlined a memory block, kmemleak scan will trigger a crash, as it
> encounters a page ext address that has already been freed during memory
> offlining. At the beginning in alloc_page_ext(), it calls
> kmemleak_alloc(), but it does not call kmemleak_free() in
> __free_page_ext().
[...]
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index 8c78b8d45117..b68f2a58ea3b 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -288,6 +288,7 @@ static void __free_page_ext(unsigned long pfn)
>  	base = get_entry(ms->page_ext, pfn);
>  	free_page_ext(base);
>  	ms->page_ext = NULL;
> +	kmemleak_free(base);
>  }

The kmemleak_free() call should be placed before free_page_ext() to
avoid a small window where the address has been freed but kmemleak not
informed.

-- 
Catalin

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