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    SubjectRe: kernel BUG at mm/rmap.c:480 in 2.6.10-rc3-bk7
    On Thu, Dec 16, 2004 at 05:18:59AM +0000, Hugh Dickins wrote:
    > going on, such avoidance may be the right course of action; but not yet.

    Yes, the real reason of my changes are quite unrelated to this bug: i.e.
    we to keep mapcount zero for all pages with page->mapping = NULL so they
    don't even enter objrmap.c, and to enforce other nice bits like that
    page-reserved must have page->mapping = NULL and other VM_RESERVED
    related enforcements. It wasn't meant to hide bugs and infact we should
    remove anything that that hides real bugs if my changes are truly hiding
    them. I still don't excude they're a real fix though, the fact I can't
    tell the exact reason why they help doesn't mean they're not fixing the
    real bug (there's quite some code in objrmap.c that definitely should
    not be involved with non-pageable pages, and my patch enforces this,
    unlike mainline).

    Infact if a page becomes suddenly unreserved, shouldn't the accounting
    break anyways at the page->count level? The page would be freed twice
    instead of once.

    I wonder if the sg_cleanup explains why some mapped reserved page
    suddenly become unreserved. Can you track if the DRM_IOCTL_SG_FREE is
    being called in a mapped vma? I guess you could start by enabling
    DRM(flags) in drm_init.h.

    #if 0
    int DRM(flags) = DRM_FLAG_DEBUG;
    #else
    int DRM(flags) = 0;
    #endif

    (set to 1 and then it should print something)
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