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Subjectfutex code and barriers
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Hi All,

While looking through the futex code I stumbled upon the following bit:

kernel/futex.c:

/* add_wait_queue is the barrier after __set_current_state. */
__set_current_state(TASK_INTERRUPTIBLE);
add_wait_queue(&q.waiters, &wait);


However,

void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
{
unsigned long flags;

wait->flags &= ~WQ_FLAG_EXCLUSIVE;
spin_lock_irqsave(&q->lock, flags);
__add_wait_queue(q, wait);
spin_unlock_irqrestore(&q->lock, flags);
}

static inline void __add_wait_queue(wait_queue_head_t *head, wait_queue_t *new)
{
list_add(&new->task_list, &head->task_list);
}

static inline void list_add(struct list_head *new, struct list_head *head)
{
__list_add(new, head, head->next);
}

static inline void __list_add(struct list_head *new,
struct list_head *prev,
struct list_head *next)
{
next->prev = new;
new->next = next;
new->prev = prev;
prev->next = new;
}

Non of which implies a full barrier.





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