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    SubjectRe: [PATCH/RFC] Futex mmap_sem deadlock
    On Wed, Feb 23, 2005 at 11:39:08AM +0000, David Howells wrote:
    > Alternately, you could just have do_page_fault() do:
    > while (!down_read_trylock(&current->mm->mmap_sem))
    > continue;
    > However, note that this can suffer from starvation due to a never ending flow
    > of mixed write-locks and read-locks on other CPUs. Unlikely, true, but not
    > impossible.

    How can this help?

    The semaphore is held for reading by the thread that faulted in
    futex_wait() -> get_user(), so no writers will be let through. Until the
    writer has been let through, the down_read_trylock will never succeed
    either. No forward progress can be made even with the above loop.

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