linux-kernel - Threaded interrupt handlers broken?

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Message-Id: <200908161153.14081.mb@bu3sch.de>
Date:	Sun, 16 Aug 2009 11:53:13 +0200
From:	Michael Buesch <mb@...sch.de>
To:	linux-kernel@...r.kernel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>
Subject: Threaded interrupt handlers broken?

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 }

-- 
Greetings, Michael.
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