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SubjectRe: [ 57/72] genirq: Unmask oneshot irqs when thread was not woken
On Tue, 6 Mar 2012, Linus Torvalds wrote:
> On Tue, Mar 6, 2012 at 12:26 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> without ever doing any insane bit scanning.

Duh, yes. That's really insane. I first did

- new->thread_mask = 1 << ffz(thread_mask);
+ new->thread_mask = (new->flags & IRQF_ONESHOT) ? 1 << ffz(thread_mask) : 0;

and then decided to move it into the already existing new->flags &
IRQF_ONESHOT check section and deleted the wrong part ....

/me looks for a huge brown paperbag.

Thanks for catching it !

tglx

-------------->
Subject: genirq: Clear action->thread_mask if IRQ_ONESHOT is not set

commit 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-by: Sven Joachim <svenjoac@gmx.de>
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---

Index: tip/kernel/irq/manage.c
===================================================================
--- tip.orig/kernel/irq/manage.c
+++ tip/kernel/irq/manage.c
@@ -985,6 +985,11 @@ __setup_irq(unsigned int irq, struct irq

/* 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
}

/*
- * 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);

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