On 06/08, Nicholas A. Bellinger wrote:
>
> +unsigned tag_alloc(struct tag_pool *pool, bool wait)
> +{
> + struct tag_cpu_freelist *tags;
> + unsigned long flags;
> + unsigned ret;
> +retry:
> + preempt_disable();
> + local_irq_save(flags);
> + tags = this_cpu_ptr(pool->tag_cpu);
> +
> + while (!tags->nr_free) {
> + spin_lock(&pool->lock);
> +
> + if (pool->nr_free)
> + move_tags(tags->free, &tags->nr_free,
> + pool->free, &pool->nr_free,
> + min(pool->nr_free, pool->watermark));
> + else if (wait) {
> + struct tag_waiter wait = { .task = current };
> +
> + __set_current_state(TASK_UNINTERRUPTIBLE);
> + list_add(&wait.list, &pool->wait);
> +
> + spin_unlock(&pool->lock);
> + local_irq_restore(flags);
> + preempt_enable();
> +
> + schedule();
> +
> + if (!list_empty_careful(&wait.list)) {
> + spin_lock_irqsave(&pool->lock, flags);
> + list_del_init(&wait.list);
> + spin_unlock_irqrestore(&pool->lock, flags);
> + }
> +
> + goto retry;
> + } else
> + goto fail;
> +
> + spin_unlock(&pool->lock);
> + }
> +
> + ret = tags->free[--tags->nr_free];
> +
> + local_irq_restore(flags);
> + preempt_enable();
> +
> + return ret;
> +fail:
> + local_irq_restore(flags);
> + preempt_enable();
> + return 0;
> +}
I still think this code should use the normal wait_event().
See http://marc.info/?l=linux-kernel&m=136863269729888
> +void tag_free(struct tag_pool *pool, unsigned tag)
> +{
> + struct tag_cpu_freelist *tags;
> + unsigned long flags;
> +
> + preempt_disable();
> + local_irq_save(flags);
> + tags = this_cpu_ptr(pool->tag_cpu);
> +
> + tags->free[tags->nr_free++] = tag;
> +
> + if (tags->nr_free == pool->watermark * 2) {
> + spin_lock(&pool->lock);
> +
> + move_tags(pool->free, &pool->nr_free,
> + tags->free, &tags->nr_free,
> + pool->watermark);
> +
> + while (!list_empty(&pool->wait)) {
> + struct tag_waiter *wait;
> + wait = list_first_entry(&pool->wait,
> + struct tag_waiter, list);
> + list_del_init(&wait->list);
> + wake_up_process(wait->task);
And this still looks racy.
see http://marc.info/?l=linux-kernel&m=136853955229504
And probably the changelog should mention that cpu_down() can
lose the tags.
Oleg.
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