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Date: Wed, 9 Feb 2011 15:40:17 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "hannes@cmpxchg.org" <hannes@cmpxchg.org>,
        "nishimura@mxp.nes.nec.co.jp" <nishimura@mxp.nes.nec.co.jp>
Subject: Re: [mmotm] BUG: Bad page state in process khugepaged ?
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On Wed, 9 Feb 2011 15:10:36 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> 2nd log, "kernel BUG at include/linux/mm.h:420!" is  This one.
> ==
> static inline void __ClearPageBuddy(struct page *page)
> {
>         VM_BUG_ON(!PageBuddy(page));
>         atomic_set(&page->_mapcount, -1);
> }
> ==
> But this is just a tail of bad_page().
> ==
> static void bad_page(struct page *page)
> {
>         static unsigned long resume;
>         static unsigned long nr_shown;
>         static unsigned long nr_unshown;
> ...
>         dump_stack();
> out:
>         /* Leave bad fields for debug, except PageBuddy could make trouble */
>         __ClearPageBuddy(page);
>         add_taint(TAINT_BAD_PAGE);
> }
> ==
> So, what important is bad_page().
> 
> BAD page says
> ==
> BUG: Bad page state in process khugepaged  pfn:1e9800
> page:ffffea0006b14000 count:0 mapcount:0 mapping:          (null) index:0x2800
> page flags: 0x40000000004000(head)
> pc:ffff880214a30000 pc->flags:2146246697418756 pc->mem_cgroup:ffffc9000177a000
> ==
> 
> Maybe page_mapcount(page) was > 0. and ->mapping was NULL.
Sorry please ignore above. bad_page() used page_mapcount().


Regards,
-Kame