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    SubjectRe: [patch 05/15] Generic Mutex Subsystem, mutex-core.patch

    * Oleg Nesterov <oleg@tv-sign.ru> wrote:

    > > + spin_lock(&lock->wait_lock);
    > > + __add_waiter(lock, waiter, ti, task __IP__);
    > > + set_task_state(task, task_state);
    >
    > I can't understand why __mutex_lock_common() does xchg() after adding
    > the waiter to the ->wait_list. We are holding ->wait_lock, we can't
    > race with __mutex_unlock_nonatomic() - it calls wake_up() and sets
    > ->count under this spinlock.

    we must make sure that the drop has not been dropped meanwhile, on the
    way in, between the fastpath-unlock atomic op, and the xchg() here.

    Ingo
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