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    SubjectRe: assert/crash in __rmqueue() when enabling CONFIG_NUMA

    * Nick Piggin <npiggin@suse.de> wrote:

    > On Wed, Apr 19, 2006 at 01:21:30PM +0200, Ingo Molnar wrote:
    > > the 2.6.17-rc2 kernel built with the attached config crashes quite
    > > easily under minimal load. Disabling CONFIG_NUMA makes it robust again.
    > > Crashlog attached.
    >
    > It would be interesting to know which assertion failed. I guess it
    > might be a zone alignment problem -- it would be interesting to turn
    > the 2 HOLES_IN_ZONE tests into BUG_ONs, and enable them (ie. move them
    > out of HOLES_IN_ZONE).

    ok, i added a couple of printks (see the patch below), and got this:

    zone c1f0a600 (HighMem):
    pfn: 00037d00
    zone->zone_start_pfn: 00037e00
    zone->spanned_pages: 00007e00
    zone->zone_start_pfn + zone->spanned_pages: 0003fc00
    ------------[ cut here ]------------
    kernel BUG at mm/page_alloc.c:524!

    so the pfn is 1MB below the zone's start address - not good. You can
    find the full bootup log at:

    http://redhat.com/~mingo/misc/crash.log

    the log should also give an idea about how the zones are layed out, etc.
    Note that this is an ordinary desktop dual-core box with 1GB RAM booting
    an allyesconfig NUMA kernel. I suspect this could be some bootup-time
    zone sizing problem? The config is at:

    http://redhat.com/~mingo/misc/config

    (the crash is easy to reproduce, so let me know if i can do anything
    else to debug this.)

    Ingo

    Index: linux/mm/page_alloc.c
    ===================================================================
    --- linux.orig/mm/page_alloc.c
    +++ linux/mm/page_alloc.c
    @@ -100,17 +100,32 @@ static int page_outside_zone_boundaries(
    ret = 1;
    } while (zone_span_seqretry(zone, seq));

    +#define P(x) printk("%s: %08lx\n", #x, x)
    +
    + if (ret) {
    + printk("zone %p (%s):\n", zone, zone->name);
    + P(pfn);
    + P(zone->zone_start_pfn);
    + P(zone->spanned_pages);
    + P(zone->zone_start_pfn + zone->spanned_pages);
    + }
    +
    return ret;
    }

    static int page_is_consistent(struct zone *zone, struct page *page)
    {
    -#ifdef CONFIG_HOLES_IN_ZONE
    - if (!pfn_valid(page_to_pfn(page)))
    + if (!pfn_valid(page_to_pfn(page))) {
    + printk("BUG: pfn: %08lx, page: %p\n",
    + page_to_pfn(page), page);
    + dump_stack();
    return 0;
    -#endif
    - if (zone != page_zone(page))
    + }
    + if (zone != page_zone(page)) {
    + printk("zone: %p != %p == page_zone(%p)\n",
    + zone, page_zone(page), page);
    return 0;
    + }

    return 1;
    }
    @@ -292,10 +307,12 @@ __find_combined_index(unsigned long page
    */
    static inline int page_is_buddy(struct page *page, int order)
    {
    -#ifdef CONFIG_HOLES_IN_ZONE
    - if (!pfn_valid(page_to_pfn(page)))
    + if (!pfn_valid(page_to_pfn(page))) {
    + printk("BUG: pfn: %08lx, page: %p, order: %d\n",
    + page_to_pfn(page), page, order);
    + dump_stack();
    return 0;
    -#endif
    + }

    if (PageBuddy(page) && page_order(page) == order) {
    BUG_ON(page_count(page) != 0);
    -
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