From: Michal Hocko <mhocko@suse.cz>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
Mel Gorman <mel@csn.ul.ie>
Subject: Re: [BUGFIX][PATCH] fix is_mem_section_removable() page_order BUG_ON check.
Date: Mon, 25 Oct 2010 15:10:25 +0200 [thread overview]
Message-ID: <20101025131025.GA18570@tiehlicka.suse.cz> (raw)
In-Reply-To: <20101025074933.GB5452@localhost>
On Mon 25-10-10 15:49:33, Wu Fengguang wrote:
> On Mon, Oct 25, 2010 at 02:37:26PM +0800, KAMEZAWA Hiroyuki wrote:
> > I wonder this should be for stable tree...but want to hear opinions before.
> > ==
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> >
> > page_order() is called by memory hotplug's user interface to check
> > the section is removable or not. (is_mem_section_removable())
> >
> > It calls page_order() withoug holding zone->lock.
> > So, even if the caller does
> >
> > if (PageBuddy(page))
> > ret = page_order(page) ...
> > The caller may hit BUG_ON().
> >
> > For fixing this, there are 2 choices.
> > 1. add zone->lock.
> > 2. remove BUG_ON().
>
> One more alternative might be to introduce a private
> maybe_page_order() for is_mem_section_removable(). Not a big deal.
I guess this is not necessary as all page_order callers check PageBuddy
anyway AFAICS.
>
> > is_mem_section_removable() is used for some "advice" and doesn't need
> > to be 100% accurate. This is_removable() can be called via user program..
> > We don't want to take this important lock for long by user's request.
> > So, this patch removes BUG_ON().
>
> Acked-by: Wu Fengguang <fengguang.wu@intel.com>
Yes, the change looks good.
--
Michal Hocko
L3 team
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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next prev parent reply other threads:[~2010-10-25 13:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-25 6:37 [BUGFIX][PATCH] fix is_mem_section_removable() page_order BUG_ON check KAMEZAWA Hiroyuki
2010-10-25 7:49 ` Wu Fengguang
2010-10-25 13:10 ` Michal Hocko [this message]
2010-10-25 13:16 ` Wu Fengguang
2010-10-25 21:24 ` Andrew Morton
2010-10-25 17:03 ` Mel Gorman
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