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    SubjectRe: [PATCH] [BUGFIX] update mm->owner even if no next owner.
    On Sat, Jun 11, 2011 at 09:04:14AM -0700, Hugh Dickins wrote:
    > I had another go at reproducing it, 2 hours that time, then a try with
    > 692e0b35427a reverted: it ran overnight for 9 hours when I stopped it.
    >
    > Andrea, please would you ask Linus to revert that commit before -rc3?
    > Or is there something else you'd like us to try instead? I admit that
    > I've not actually taken the time to think through exactly how it goes
    > wrong, but it does look dangerous.

    Here I was asked if the mem_cgroup_newpage_charge need the mmap_sem at
    all. And if not why not to release the mmap_sem early.

    https://lkml.org/lkml/2011/3/14/276

    So I didn't see why mmap_sem was needed, I also asked confirmation and
    who answered agreed it was safe without mmap_sem even if it's the only
    place doing that. Maybe that assumption was wrong and we need
    mmap_sem after all if this commit is causing problems.

    Or did you find something wrong in the actual patch?

    Do I understand right that the bug just that we must run
    alloc_hugepage_vma+mem_cgroup_newpage_charge within the same critical
    section protected by the mmap_sem read mode? Do we know why?

    > The way I reproduce it is with my tmpfs kbuilds swapping load,
    > in this case restricting mem by memcg, and (perhaps the important
    > detail, not certain) doing concurrent swapoff/swapon repeatedly -
    > swapoff takes another mm_users reference to the mm it's working on,
    > which can cause surprises.

    Ok.


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