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    SubjectRe: kernel BUG at mm/memory.c:1228!
    On Wed, 6 Jun 2012, Dave Jones wrote:

    > I hit this in overnight testing..
    >
    > ------------[ cut here ]------------
    > kernel BUG at mm/memory.c:1228!

    Looks like a duplicate of the "mm: kernel BUG at mm/memory.c:1230" thread
    at http://marc.info/?t=133788420400003

    Andrea suggested adding a printk of addr, end, vma->vm_start, and
    vma->vm_end to debug it.

    Since it's been reported a few different times, perhaps this should be
    merged?


    mm, thp: print useful information when mmap_sem is unlocked in zap_pmd_range

    Andrea asked for addr, end, vma->vm_start, and vma->vm_end to be emitted
    when !rwsem_is_locked(&tlb->mm->mmap_sem). Otherwise, debugging the
    underlying issue is more difficult.

    Signed-off-by: David Rientjes <rientjes@google.com>
    ---
    mm/memory.c | 10 +++++++++-
    1 file changed, 9 insertions(+), 1 deletion(-)

    diff --git a/mm/memory.c b/mm/memory.c
    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -1225,7 +1225,15 @@ static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
    next = pmd_addr_end(addr, end);
    if (pmd_trans_huge(*pmd)) {
    if (next - addr != HPAGE_PMD_SIZE) {
    - VM_BUG_ON(!rwsem_is_locked(&tlb->mm->mmap_sem));
    +#ifdef CONFIG_DEBUG_VM
    + if (!rwsem_is_locked(&tlb->mm->mmap_sem)) {
    + pr_err("%s: mmap_sem is unlocked! addr=%lu end=%lu vma->vm_start=%lu vma->vm_end=%lu\n",
    + __func__, addr, end,
    + vma->vm_start,
    + vma->vm_end);
    + BUG();
    + }
    +#endif
    split_huge_page_pmd(vma->vm_mm, pmd);
    } else if (zap_huge_pmd(tlb, vma, pmd, addr))
    goto next;

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