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    SubjectRe: [PATCH 2/5] HWPOISON: fix tasklist_lock/anon_vma locking order
    On Fri, Jun 12, 2009 at 12:03:08PM +0200, Andi Kleen wrote:
    > On Thu, Jun 11, 2009 at 10:22:41PM +0800, Wu Fengguang wrote:
    > > To avoid possible deadlock. Proposed by Nick Piggin:
    >
    > I disagree with the description. There's no possible deadlock right now.
    > It would be purely out of paranoia.
    >
    > >
    > > You have tasklist_lock(R) nesting outside i_mmap_lock, and inside anon_vma
    > > lock. And anon_vma lock nests inside i_mmap_lock.
    > >
    > > This seems fragile. If rwlocks ever become FIFO or tasklist_lock changes
    >
    > I was a bit dubious on this reasoning. If rwlocks become FIFO a lot of
    > stuff will likely break.
    >
    > > type (maybe -rt kernels do it), then you could have a task holding
    >
    > I think they tried but backed off quickly again
    >
    > It's ok with a less scare-mongering description.

    There's simply no good reason to invert ordering of locks like
    this.



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