genirq: Clear action->thread_mask if IRQ_ONESHOT is not set
Thomas Gleixner [Tue, 6 Mar 2012 22:18:54 +0000 (23:18 +0100)]
Xommit ac5637611(genirq: Unmask oneshot irqs when thread was not woken)
fails to unmask when a !IRQ_ONESHOT threaded handler is handled by
handle_level_irq.

This happens because thread_mask is or'ed unconditionally in
irq_wake_thread(), but for !IRQ_ONESHOT interrupts never cleared.  So
the check for !desc->thread_active fails and keeps the interrupt
disabled.

Keep the thread_mask zero for !IRQ_ONESHOT interrupts.

Document the thread_mask magic while at it.

Reported-and-tested-by: Sven Joachim <svenjoac@gmx.de>
Reported-and-tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/irq/manage.c

index 32313c0..0f0d470 100644 (file)
@@ -985,6 +985,11 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
 
                /* add new interrupt at end of irq queue */
                do {
+                       /*
+                        * Or all existing action->thread_mask bits,
+                        * so we can find the next zero bit for this
+                        * new action.
+                        */
                        thread_mask |= old->thread_mask;
                        old_ptr = &old->next;
                        old = *old_ptr;
@@ -993,14 +998,41 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
        }
 
        /*
-        * Setup the thread mask for this irqaction. Unlikely to have
-        * 32 resp 64 irqs sharing one line, but who knows.
+        * Setup the thread mask for this irqaction for ONESHOT. For
+        * !ONESHOT irqs the thread mask is 0 so we can avoid a
+        * conditional in irq_wake_thread().
         */
-       if (new->flags & IRQF_ONESHOT && thread_mask == ~0UL) {
-               ret = -EBUSY;
-               goto out_mask;
+       if (new->flags & IRQF_ONESHOT) {
+               /*
+                * Unlikely to have 32 resp 64 irqs sharing one line,
+                * but who knows.
+                */
+               if (thread_mask == ~0UL) {
+                       ret = -EBUSY;
+                       goto out_mask;
+               }
+               /*
+                * The thread_mask for the action is or'ed to
+                * desc->thread_active to indicate that the
+                * IRQF_ONESHOT thread handler has been woken, but not
+                * yet finished. The bit is cleared when a thread
+                * completes. When all threads of a shared interrupt
+                * line have completed desc->threads_active becomes
+                * zero and the interrupt line is unmasked. See
+                * handle.c:irq_wake_thread() for further information.
+                *
+                * If no thread is woken by primary (hard irq context)
+                * interrupt handlers, then desc->threads_active is
+                * also checked for zero to unmask the irq line in the
+                * affected hard irq flow handlers
+                * (handle_[fasteoi|level]_irq).
+                *
+                * The new action gets the first zero bit of
+                * thread_mask assigned. See the loop above which or's
+                * all existing action->thread_mask bits.
+                */
+               new->thread_mask = 1 << ffz(thread_mask);
        }
-       new->thread_mask = 1 << ffz(thread_mask);
 
        if (!shared) {
                init_waitqueue_head(&desc->wait_for_threads);