On 13-12-12 06:18 AM, Peter Zijlstra wrote:
> On Wed, Dec 11, 2013 at 08:06:37PM -0500, Paul Gortmaker wrote:
>> +/*
>> + * Event API
>> + */
>> +#define __swait_event(wq, condition)
>> \
>> +do {
>> \
>> + DEFINE_SWAITER(__wait); \
>> + \
>> + for (;;) { \
>> + swait_prepare(&wq, &__wait, TASK_UNINTERRUPTIBLE); \
>> + if (condition) \
>> + break; \
>> + schedule(); \
>> + } \
>> + swait_finish(&wq, &__wait); \
>> +} while (0)
>> +
>> +#define __swait_event_interruptible(wq, condition, ret)
>> \
>> +do {
>> \
>> + DEFINE_SWAITER(__wait); \
>> + \
>> + for (;;) { \
>> + swait_prepare(&wq, &__wait, TASK_INTERRUPTIBLE); \
>> + if (condition) \
>> + break; \
>> + if (signal_pending(current)) { \
>> + ret = -ERESTARTSYS; \
>> + break; \
>> + } \
>> + schedule(); \
>> + } \
>> + swait_finish(&wq, &__wait); \
>> +} while (0)
>> +
>> +#define __swait_event_interruptible_timeout(wq, condition, ret)
>> \
>> +do {
>> \
>> + DEFINE_SWAITER(__wait); \
>> + \
>> + for (;;) { \
>> + swait_prepare(&wq, &__wait, TASK_INTERRUPTIBLE); \
>> + if (condition) \
>> + break; \
>> + if (signal_pending(current)) { \
>> + ret = -ERESTARTSYS; \
>> + break; \
>> + } \
>> + ret = schedule_timeout(ret); \
>> + if (!ret) \
>> + break; \
>> + } \
>> + swait_finish(&wq, &__wait); \
>> +} while (0)
>
> Urgh, please have a look at ___wait_event() we just killed all the
> pointless replication for the normal waitqueues, please don't add more
> of it.
Right, I recall seeing that series go by in October ; thanks for
the reminder, I'll clean this up to match what was done in commit
41a1431b178c3b73 and its follow-on commits.
Paul.
--
>
>
>> +unsigned int
>> +__swake_up_locked(struct swait_queue_head *head, unsigned int state,
>> + unsigned int num)
>> +{
>> + struct swaiter *curr, *next;
>> + int woken = 0;
>> +
>> + list_for_each_entry_safe(curr, next, &head->task_list, node) {
>> + if (wake_up_state(curr->task, state)) {
>> + __swait_dequeue(curr);
>> + /*
>> + * The waiting task can free the waiter as
>> + * soon as curr->task = NULL is written,
>> + * without taking any locks. A memory barrier
>> + * is required here to prevent the following
>> + * store to curr->task from getting ahead of
>> + * the dequeue operation.
>> + */
>> + smp_wmb();
>> + curr->task = NULL;
>> + if (++woken == num)
>> + break;
>> + }
>> + }
>> + return woken;
>> +}
>> +
>> +unsigned int
>> +__swake_up(struct swait_queue_head *head, unsigned int state, unsigned int
>> num)
>> +{
>> + unsigned long flags;
>> + int woken;
>> +
>> + if (!swaitqueue_active(head))
>> + return 0;
>> +
>> + raw_spin_lock_irqsave(&head->lock, flags);
>> + woken = __swake_up_locked(head, state, num);
>> + raw_spin_unlock_irqrestore(&head->lock, flags);
>> + return woken;
>> +}
>> +EXPORT_SYMBOL(__swake_up);
>
> Urgh, fail. Do not put unbounded loops in raw_spin_lock.
>
> I think I posted a patch a while back to cure this.
>
>
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