linux-kernel - Re: [PATCH v2 1/5] mm/memory-failure: unlock_page before put

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Date:	Fri, 31 Jul 2015 13:54:18 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Dean Nelson <dnelson@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hugh Dickins <hughd@...gle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH v2 1/5] mm/memory-failure: unlock_page before put_page

On Fri, 31 Jul 2015, Naoya Horiguchi wrote:

> In "just unpoisoned" path, we do put_page and then unlock_page, which is a
> wrong order and causes "freeing locked page" bug. So let's fix it.
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> ---
>  mm/memory-failure.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git v4.2-rc4.orig/mm/memory-failure.c v4.2-rc4/mm/memory-failure.c
> index c53543d89282..04d677048af7 100644
> --- v4.2-rc4.orig/mm/memory-failure.c
> +++ v4.2-rc4/mm/memory-failure.c
> @@ -1209,9 +1209,9 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
>  	if (!PageHWPoison(p)) {
>  		printk(KERN_ERR "MCE %#lx: just unpoisoned\n", pfn);
>  		atomic_long_sub(nr_pages, &num_poisoned_pages);
> +		unlock_page(hpage);
>  		put_page(hpage);
> -		res = 0;
> -		goto out;
> +		return 0;
>  	}
>  	if (hwpoison_filter(p)) {
>  		if (TestClearPageHWPoison(p))

Looks like you could do the unlock_page() before either the printk or 
atomic_long_sub(), but probably not important.

Acked-by: David Rientjes <rientjes@...gle.com>
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