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/*
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/*
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 * Note about race conditions.
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 * Note about race conditions.
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 * Because of non-atomic nature of operations performed sequentially on the futex
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 * Because of non-atomic nature of operations performed sequentially on the futex
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 * counter and the futex wait queue, there is a race condition:
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 * counter and the futex wait queue, there is a race condition:
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 *
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 *
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 * wq->missed_wakeups == 1 && futex->count = 1
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 * (wq->missed_wakeups == 1) && (futex->count = 1)
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 *
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 *
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 * Scenario 1 (wait queue timeout vs. futex_up()):
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 * Scenario 1 (wait queue timeout vs. futex_up()):
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 * 1. assume wq->missed_wakeups == 0 && futex->count == -1
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 * 1. assume wq->missed_wakeups == 0 && futex->count == -1
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 *    (ie. thread A sleeping, thread B in the critical section)
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 *    (ie. thread A sleeping, thread B in the critical section)
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 * 2. A receives timeout and gets removed from the wait queue
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 * 2. A receives timeout and gets removed from the wait queue
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/** Up the futex.
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/** Up the futex.
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 *
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 *
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 * @param futex Futex.
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 * @param futex Futex.
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 *
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 *
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 * @return ENOENT if there is no such virtual address or futex. Otherwise zero.
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 * @return ENOENT if there is no such virtual address. Otherwise zero.
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 */
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 */
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int futex_up(atomic_t *futex)
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int futex_up(atomic_t *futex)
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{
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{
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    long val;
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    long val;
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