linux-kernel - Re: [PATCH] mm/hwpoison: fix page refcount of unkown non LRU page

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Date:	Fri, 7 Aug 2015 07:46:13 +0000
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Wanpeng Li <wanpeng.li@...mail.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Tony Luck <tony.luck@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] mm/hwpoison: fix page refcount of unkown non LRU page

On Thu, Aug 06, 2015 at 04:09:37PM +0800, Wanpeng Li wrote:
> After try to drain pages from pagevec/pageset, we try to get reference
> count of the page again, however, the reference count of the page is 
> not reduced if the page is still not on LRU list. This patch fix it by 
> adding the put_page() to drop the page reference which is from 
> __get_any_page().
> 
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com> 

This fix is correct. Thanks you for catching this, Wanpeng!

Acked-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>

BTW, I think this patch is worth sending to stable tree. It seems that
the latest change around this code is given by the following commit:

  commit af8fae7c08862bb85c5cf445bf9b36314b82111f
  Author: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
  Date:   Fri Feb 22 16:34:03 2013 -0800
  
      mm/memory-failure.c: clean up soft_offline_page()

. I think that this bug existed before this commit, but this patch is
cleanly applicable only after this patch, so I think tagging
"Cc: stable@...r.kernel.org # 3.9+" is good.

Thanks,
Naoya Horiguchi

> ---
>  mm/memory-failure.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index c53543d..23163d0 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1535,6 +1535,8 @@ static int get_any_page(struct page *page, unsigned long pfn, int flags)
>  		 */
>  		ret = __get_any_page(page, pfn, 0);
>  		if (!PageLRU(page)) {
> +			/* Drop page reference which is from __get_any_page() */
> +			put_page(page);
>  			pr_info("soft_offline: %#lx: unknown non LRU page type %lx\n",
>  				pfn, page->flags);
>  			return -EIO;
> -- 
> 1.7.1
> --
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