Threaded interrupt handlers broken?

Michael Buesch
2009-08-16T09:54:05Z

Hi,

I was trying to use threaded interrupt handlers, but the code always crashes
within irq_thread() with a "BUG: spinlock bad magic 00000000".
The spinlock that's not properly initialized is from the wait_for_threads waitqueue.
It crashes on line 526 (see below).
The initialization of the waitqueue struct seems to depend on whether the IRQ is
shared or not. I don't know if that's correct, but I patched it to unconditionally
initialize the struct. That did not help.

Any ideas?

490 static int irq_thread(void *data)
491 {
492 struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO/2, };
493 struct irqaction *action = data;
494 struct irq_desc *desc = irq_to_desc(action->irq);
495 int wake;
496
497 sched_setscheduler(current, SCHED_FIFO, &param);
498 current->irqaction = action;
499
500 while (!irq_wait_for_interrupt(action)) {
501
502 irq_thread_check_affinity(desc, action);
503
504 atomic_inc(&desc->threads_active);
505
506 spin_lock_irq(&desc->lock);
507 if (unlikely(desc->status & IRQ_DISABLED)) {
508 /*
509 * CHECKME: We might need a dedicated
510 * IRQ_THREAD_PENDING flag here, which
511 * retriggers the thread in check_irq_resend()
512 * but AFAICT IRQ_PENDING should be fine as it
513 * retriggers the interrupt itself --- tglx
514 */
515 desc->status |= IRQ_PENDING;
516 spin_unlock_irq(&desc->lock);
517 } else {
518 spin_unlock_irq(&desc->lock);
519
520 action->thread_fn(action->irq, action->dev_id);
521 }
522
523 wake = atomic_dec_and_test(&desc->threads_active);
524
525 if (wake && waitqueue_active(&desc->wait_for_threads))
526 wake_up(&desc->wait_for_threads); <<<<<<<<<<<<<<<<<<<<<<<<
527 }
528
529 /*
530 * Clear irqaction. Otherwise exit_irq_thread() would make
531 * fuzz about an active irq thread going into nirvana.
532 */
533 current->irqaction = NULL;
534 return 0;
535 }