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authorThomas Gleixner <tglx@linutronix.de>2011-02-23 23:52:13 +0000
committerThomas Gleixner <tglx@linutronix.de>2011-02-25 20:24:21 +0100
commitb5faba21a6805c33b40e258d36f57997ee1de131 (patch)
treec84ef3357ecd6e1b1cfda623136529db0e5fab6f /kernel/irq/handle.c
parent1204e95689f9fbd245a4ce5c1b0cd0a9b77f8d25 (diff)
downloadlinux-stericsson-b5faba21a6805c33b40e258d36f57997ee1de131.tar.gz
genirq: Prepare the handling of shared oneshot interrupts
For level type interrupts we need to track how many threads are on flight to avoid useless interrupt storms when not all thread handlers have finished yet. Keep track of the woken threads and only unmask when there are no more threads in flight. Yes, I'm lazy and using a bitfield. But not only because I'm lazy, the main reason is that it's way simpler than using a refcount. A refcount based solution would need to keep track of various things like crashing the irq thread, spurious interrupts coming in, disables/enables, free_irq() and some more. The bitfield keeps the tracking simple and makes things just work. It's also nicely confined to the thread code pathes and does not require additional checks all over the place. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> LKML-Reference: <20110223234956.388095876@linutronix.de>
Diffstat (limited to 'kernel/irq/handle.c')
-rw-r--r--kernel/irq/handle.c76
1 files changed, 63 insertions, 13 deletions
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index b110c835e070..517561fc7317 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -51,6 +51,68 @@ static void warn_no_thread(unsigned int irq, struct irqaction *action)
"but no thread function available.", irq, action->name);
}
+static void irq_wake_thread(struct irq_desc *desc, struct irqaction *action)
+{
+ /*
+ * Wake up the handler thread for this action. In case the
+ * thread crashed and was killed we just pretend that we
+ * handled the interrupt. The hardirq handler has disabled the
+ * device interrupt, so no irq storm is lurking. If the
+ * RUNTHREAD bit is already set, nothing to do.
+ */
+ if (test_bit(IRQTF_DIED, &action->thread_flags) ||
+ test_and_set_bit(IRQTF_RUNTHREAD, &action->thread_flags))
+ return;
+
+ /*
+ * It's safe to OR the mask lockless here. We have only two
+ * places which write to threads_oneshot: This code and the
+ * irq thread.
+ *
+ * This code is the hard irq context and can never run on two
+ * cpus in parallel. If it ever does we have more serious
+ * problems than this bitmask.
+ *
+ * The irq threads of this irq which clear their "running" bit
+ * in threads_oneshot are serialized via desc->lock against
+ * each other and they are serialized against this code by
+ * IRQS_INPROGRESS.
+ *
+ * Hard irq handler:
+ *
+ * spin_lock(desc->lock);
+ * desc->state |= IRQS_INPROGRESS;
+ * spin_unlock(desc->lock);
+ * set_bit(IRQTF_RUNTHREAD, &action->thread_flags);
+ * desc->threads_oneshot |= mask;
+ * spin_lock(desc->lock);
+ * desc->state &= ~IRQS_INPROGRESS;
+ * spin_unlock(desc->lock);
+ *
+ * irq thread:
+ *
+ * again:
+ * spin_lock(desc->lock);
+ * if (desc->state & IRQS_INPROGRESS) {
+ * spin_unlock(desc->lock);
+ * while(desc->state & IRQS_INPROGRESS)
+ * cpu_relax();
+ * goto again;
+ * }
+ * if (!test_bit(IRQTF_RUNTHREAD, &action->thread_flags))
+ * desc->threads_oneshot &= ~mask;
+ * spin_unlock(desc->lock);
+ *
+ * So either the thread waits for us to clear IRQS_INPROGRESS
+ * or we are waiting in the flow handler for desc->lock to be
+ * released before we reach this point. The thread also checks
+ * IRQTF_RUNTHREAD under desc->lock. If set it leaves
+ * threads_oneshot untouched and runs the thread another time.
+ */
+ desc->threads_oneshot |= action->thread_mask;
+ wake_up_process(action->thread);
+}
+
irqreturn_t
handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
{
@@ -85,19 +147,7 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
break;
}
- /*
- * Wake up the handler thread for this
- * action. In case the thread crashed and was
- * killed we just pretend that we handled the
- * interrupt. The hardirq handler above has
- * disabled the device interrupt, so no irq
- * storm is lurking.
- */
- if (likely(!test_bit(IRQTF_DIED,
- &action->thread_flags))) {
- set_bit(IRQTF_RUNTHREAD, &action->thread_flags);
- wake_up_process(action->thread);
- }
+ irq_wake_thread(desc, action);
/* Fall through to add to randomness */
case IRQ_HANDLED: