[tip:irq/core] genirq: Allow migration of chained interrupts by installing default action

[tip-bot for Mika Westerberg]

Commit-ID:  e509bd7da149dc34916037484cd7545b2d48a2b0
Gitweb:     http://git.kernel.org/tip/e509bd7da149dc34916037484cd7545b2d48a2b0
Author:     Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
AuthorDate: Mon, 5 Oct 2015 13:12:15 +0300
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 9 Oct 2015 22:47:27 +0200

genirq: Allow migration of chained interrupts by installing default action

When a CPU is offlined all interrupts that have an action are migrated to
other still online CPUs. However, if the interrupt has chained handler
installed this is not done. Chained handlers are used by GPIO drivers which
support interrupts, for instance.

When the affinity is not corrected properly we end up in situation where
most interrupts are not arriving to the online CPUs anymore. For example on
Intel Braswell system which has SD-card card detection signal connected to
a GPIO the IO-APIC routing entries look like below after CPU1 is offlined:

  pin30, enabled , level, low , V(52), IRR(0), S(0), logical , D(03), M(1)
  pin31, enabled , level, low , V(42), IRR(0), S(0), logical , D(03), M(1)
  pin32, enabled , level, low , V(62), IRR(0), S(0), logical , D(03), M(1)
  pin5b, enabled , level, low , V(72), IRR(0), S(0), logical , D(03), M(1)

The problem here is that the destination mask still contains both CPUs even
if CPU1 is already offline. This means that the IO-APIC still routes
interrupts to the other CPU as well.

We solve the problem by providing a default action for chained interrupts.
This action allows the migration code to correct affinity (as it finds
desc->action != NULL).

Also make the default action handler to emit a warning if for some reason a
chained handler ends up calling it.

Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
Cc: Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1444039935-30475-1-git-send-email-mika.westerberg@xxxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 kernel/irq/chip.c      | 17 +++++++++++++++++
 kernel/irq/internals.h |  2 ++
 kernel/irq/proc.c      |  2 +-
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index 46f1fb5..4aa00d3 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -21,6 +21,20 @@
 
 #include "internals.h"
 
+static irqreturn_t bad_chained_irq(int irq, void *dev_id)
+{
+	WARN_ONCE(1, "Chained irq %d should not call an action\n", irq);
+	return IRQ_NONE;
+}
+
+/*
+ * Chained handlers should never call action on their IRQ. This default
+ * action will emit warning if such thing happens.
+ */
+struct irqaction chained_action = {
+	.handler = bad_chained_irq,
+};
+
 /**
  *	irq_set_chip - set the irq chip for an irq
  *	@irq:	irq number
@@ -746,6 +760,8 @@ __irq_do_set_handler(struct irq_desc *desc, irq_flow_handler_t handle,
 		if (desc->irq_data.chip != &no_irq_chip)
 			mask_ack_irq(desc);
 		irq_state_set_disabled(desc);
+		if (is_chained)
+			desc->action = NULL;
 		desc->depth = 1;
 	}
 	desc->handle_irq = handle;
@@ -755,6 +771,7 @@ __irq_do_set_handler(struct irq_desc *desc, irq_flow_handler_t handle,
 		irq_settings_set_noprobe(desc);
 		irq_settings_set_norequest(desc);
 		irq_settings_set_nothread(desc);
+		desc->action = &chained_action;
 		irq_startup(desc, true);
 	}
 }
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index cd60bb4..05c2188 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -18,6 +18,8 @@
 
 extern bool noirqdebug;
 
+extern struct irqaction chained_action;
+
 /*
  * Bits used by threaded handlers:
  * IRQTF_RUNTHREAD - signals that the interrupt handler thread should run
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index e3a8c95..7d60905 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -460,7 +460,7 @@ int show_interrupts(struct seq_file *p, void *v)
 	for_each_online_cpu(j)
 		any_count |= kstat_irqs_cpu(i, j);
 	action = desc->action;
-	if (!action && !any_count)
+	if ((!action || action == &chained_action) && !any_count)
 		goto out;
 
 	seq_printf(p, "%*d: ", prec, i);
--
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