Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
From: Minchan Kim <minchan@kernel.org>
To: "Shi, Yang" <yang.shi@linaro.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linaro-kernel@lists.linaro.org,
	Tang Chen <tangchen@cn.fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [PATCH] mm: check the return value of lookup_page_ext for all call sites
Date: Mon, 30 May 2016 15:11:17 +0900
Message-ID: <20160530061117.GB28624@bbox> (raw)
In-Reply-To: <aa33f1e4-5a91-aaaf-70f1-557148b29b38@linaro.org>

On Fri, May 27, 2016 at 11:16:41AM -0700, Shi, Yang wrote:

<snip>

> >
> >If we goes this way, how to guarantee this race?
> 
> Thanks for pointing out this. It sounds reasonable. However, this
> should be only possible to happen on 32 bit since just 32 bit
> version page_is_idle() calls lookup_page_ext(), it doesn't do it on
> 64 bit.
> 
> And, such race condition should exist regardless of whether DEBUG_VM
> is enabled or not, right?
> 
> rcu might be good enough to protect it.
> 
> A quick fix may look like:
> 
> diff --git a/include/linux/page_idle.h b/include/linux/page_idle.h
> index 8f5d4ad..bf0cd6a 100644
> --- a/include/linux/page_idle.h
> +++ b/include/linux/page_idle.h
> @@ -77,8 +77,12 @@ static inline bool
> test_and_clear_page_young(struct page *page)
>  static inline bool page_is_idle(struct page *page)
>  {
>         struct page_ext *page_ext;
> +
> +       rcu_read_lock();
>         page_ext = lookup_page_ext(page);
> +       rcu_read_unlock();
> +
> 	if (unlikely(!page_ext))
>                 return false;
> 
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index 56b160f..94927c9 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -183,7 +183,6 @@ struct page_ext *lookup_page_ext(struct page *page)
>  {
>         unsigned long pfn = page_to_pfn(page);
>         struct mem_section *section = __pfn_to_section(pfn);
> -#if defined(CONFIG_DEBUG_VM) || defined(CONFIG_PAGE_POISONING)
>         /*
>          * The sanity checks the page allocator does upon freeing a
>          * page can reach here before the page_ext arrays are
> @@ -195,7 +194,7 @@ struct page_ext *lookup_page_ext(struct page *page)
>          */
>         if (!section->page_ext)
>                 return NULL;
> -#endif
> +
>         return section->page_ext + pfn;
>  }
> 
> @@ -279,7 +278,8 @@ static void __free_page_ext(unsigned long pfn)
>                 return;
>         base = ms->page_ext + pfn;
>         free_page_ext(base);
> -       ms->page_ext = NULL;
> +       rcu_assign_pointer(ms->page_ext, NULL);
> +       synchronize_rcu();

How does it fix the problem?
I cannot understand your point.

>  }
> 
>  static int __meminit online_page_ext(unsigned long start_pfn,
> 
> Thanks,
> Yang
> 
> >
> >                                kpageflags_read
> >                                stable_page_flags
> >                                page_is_idle
> >                                  lookup_page_ext
> >                                  section = __pfn_to_section(pfn)
> >offline_pages
> >memory_notify(MEM_OFFLINE)
> >  offline_page_ext
> >  ms->page_ext = NULL
> >                                  section->page_ext + pfn
> >
> >>
> >>Thanks.
> >>
> 

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-23 17:16 Yang Shi
2016-05-24  2:58 ` Minchan Kim
2016-05-26  0:37   ` Minchan Kim
2016-05-26 23:15     ` Shi, Yang
2016-05-27  5:14       ` Minchan Kim
2016-05-27  6:08         ` Joonsoo Kim
2016-05-27  8:11           ` Minchan Kim
2016-05-27 18:16             ` Shi, Yang
2016-05-30  6:11               ` Minchan Kim [this message]
2016-06-01 20:40                 ` Shi, Yang
2016-06-02  5:00                   ` Minchan Kim
2016-06-02 23:15                     ` Shi, Yang
2016-05-30  5:39             ` Joonsoo Kim
2016-05-30  6:08               ` Minchan Kim
2016-06-01 20:52                 ` Shi, Yang
2016-05-27 20:02       ` Andrew Morton
2016-05-27 20:17         ` Shi, Yang
2016-05-27 20:30           ` Andrew Morton
2016-05-24 10:08 ` [PATCH] mm: fix build problems from lookup_page_ext Arnd Bergmann
2016-05-24 16:33   ` Shi, Yang
2016-05-25  7:12 ` [PATCH] mm: check the return value of lookup_page_ext for all call sites shakil
2016-05-30  6:17 ` Minchan Kim

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20160530061117.GB28624@bbox \
    --to=minchan@kernel.org \
    --cc=akpm@linux-foundation.org \
    --cc=iamjoonsoo.kim@lge.com \
    --cc=isimatu.yasuaki@jp.fujitsu.com \
    --cc=kamezawa.hiroyu@jp.fujitsu.com \
    --cc=linaro-kernel@lists.linaro.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=tangchen@cn.fujitsu.com \
    --cc=yang.shi@linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org
	public-inbox-index linux-mm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git