kernel BUG in page_alloc.c (rmqueue function)

[Steffen Persvold]

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Hi all,

Lately I've been struggeling with kernels Oopsing in page_alloc.c, 
rmqueue() function. The line which triggers the Oops is actually in 
expand() which is inlined from rmqueue() (and others). In my kernel source 
(2.4.20-pre11), expand looks like this :

#define MARK_USED(index, order, area) \
        __change_bit((index) >> (1+(order)), (area)->map)

static inline struct page * expand (zone_t *zone, struct page *page,
         unsigned long index, int low, int high, free_area_t * area)
{
        unsigned long size = 1 << high;

        while (high > low) {
                if (BAD_RANGE(zone,page))
                        BUG();
                area--;
                high--;
                size >>= 1;
                list_add(&(page)->list, &(area)->free_list);
                MARK_USED(index, high, area);
                index += size;
                page += size;
        }
        if (BAD_RANGE(zone,page))
                BUG();
        return page;
}

The line that triggers the BUG is the last BAD_RANGE check. The module 
that calls __alloc_pages() is doing it in the following way :

addr = __get_free_page(GFP_KERNEL);

and frees the page with free_page(addr);

The machine configuration is RedHat 7.3 (gcc-2.96-110, 
binutils-2.11.93.0.2-11), 2 Xeon processors @ 2.2 GHz and 2GB RAM.

The module in question is not a part of the kernel tree, but the source is 
available if someone is interested. However, I'm really interrested in 
situations that could cause BAD_RANGE() to fail (since it is commented 
with a "Temporary debugging check") because of the above usage (which 
seems very straight forward to me).

The really strange thing is that the problem seem to disappear if I apply 
the per_cpu_pages patch by Ingo Molnar as found in the RedHat 
2.4.18-17.7.x kernel with a few modifications to make it fit on 
2.4.20-pre11 (attached).

Any help greatly appreciated.

Thanks,
 -- 
  Steffen Persvold   |       Scali AS      
 mailto:[e-mail] |  http://www.scali.com
Tel: [phone] |   Olaf Helsets vei 6
Fax: [phone] |   N0621 Oslo, NORWAY

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