On Wed, 9 Feb 2011 15:10:36 +0900
KAMEZAWA Hiroyuki [off-list ref] 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





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