[PATCH v4] x86/irq: handle chained interrupts during IRQ migration

[Sundar Iyer <sundar.iyer@intel.com>]

Chained interrupt handlers dont have an irqaction and hence are not handled
during migrating interrupts when some cores go offline.

Handle this by introducing a irq_is_chained() check which is based on the the
CHAINED flag being set for such interrupts. fixup_irq() can then handle such
interrupts and not skip them over.

---
v1: use accessors instead of new variables to identify chained irqs
v2: use a mask of NOREQUEST, NOPROBE, and NOTHREAD accessor flags as per Paul M
v3: use a new accessor called IRQ_CHAINED instead of the mask in v2
v4: rebase against tip/irq/core branch

Signed-off-by: Sundar Iyer <sundar.iyer@intel.com>
Reviewed-by: Yang, Fei <fei.yang@intel.com>
Tested-by: Ng, Cheon-woei <cheon-woei.ng@intel.com>
---
 arch/x86/kernel/irq.c   |   10 ++++++----
 include/linux/irq.h     |    1 +
 include/linux/irqdesc.h |    7 +++++++
 kernel/irq/chip.c       |    1 +
 kernel/irq/settings.h   |    8 ++++++++
 5 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 3dafc60..352de40 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -255,10 +255,12 @@ void fixup_irqs(void)
 
 		data = irq_desc_get_irq_data(desc);
 		affinity = data->affinity;
-		if (!irq_has_action(irq) || irqd_is_per_cpu(data) ||
-		    cpumask_subset(affinity, cpu_online_mask)) {
-			raw_spin_unlock(&desc->lock);
-			continue;
+		/* include IRQs who have no action, but are chained */
+		if ((!irq_has_action(irq) && !irq_is_chained(irq)) ||
+			irqd_is_per_cpu(data) ||
+			cpumask_subset(affinity, cpu_online_mask)) {
+				raw_spin_unlock(&desc->lock);
+				continue;
 		}
 
 		/*
diff --git a/include/linux/irq.h b/include/linux/irq.h
index 61f5cec..531fa31 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -97,6 +97,7 @@ enum {
 	IRQ_NESTED_THREAD	= (1 << 15),
 	IRQ_NOTHREAD		= (1 << 16),
 	IRQ_PER_CPU_DEVID	= (1 << 17),
+	IRQ_CHAINED		= (1 << 18),
 };
 
 #define IRQF_MODIFY_MASK	\
diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index f1e2527..785d608 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -123,6 +123,13 @@ static inline int irq_has_action(unsigned int irq)
 	return desc->action != NULL;
 }
 
+/* Test to see if the IRQ is chained */
+static inline int irq_is_chained(unsigned int irq)
+{
+	struct irq_desc *desc = irq_to_desc(irq);
+	return desc->status_use_accessors & IRQ_CHAINED;
+}
+
 /* caller has locked the irq_desc and both params are valid */
 static inline void __irq_set_handler_locked(unsigned int irq,
 					    irq_flow_handler_t handler)
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index eebd6d5..41e0208 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -657,6 +657,7 @@ __irq_set_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained,
 		irq_settings_set_noprobe(desc);
 		irq_settings_set_norequest(desc);
 		irq_settings_set_nothread(desc);
+		irq_settings_set_chained(desc);
 		irq_startup(desc, true);
 	}
 out:
diff --git a/kernel/irq/settings.h b/kernel/irq/settings.h
index 1162f10..bb8e167 100644
--- a/kernel/irq/settings.h
+++ b/kernel/irq/settings.h
@@ -15,6 +15,7 @@ enum {
 	_IRQ_NESTED_THREAD	= IRQ_NESTED_THREAD,
 	_IRQ_PER_CPU_DEVID	= IRQ_PER_CPU_DEVID,
 	_IRQF_MODIFY_MASK	= IRQF_MODIFY_MASK,
+	_IRQ_CHAINED		= IRQ_CHAINED,
 };
 
 #define IRQ_PER_CPU		GOT_YOU_MORON
@@ -28,6 +29,7 @@ enum {
 #define IRQ_PER_CPU_DEVID	GOT_YOU_MORON
 #undef IRQF_MODIFY_MASK
 #define IRQF_MODIFY_MASK	GOT_YOU_MORON
+#define IRQ_CHAINED		GOT_YOU_MORON
 
 static inline void
 irq_settings_clr_and_set(struct irq_desc *desc, u32 clr, u32 set)
@@ -147,3 +149,9 @@ static inline bool irq_settings_is_nested_thread(struct irq_desc *desc)
 {
 	return desc->status_use_accessors & _IRQ_NESTED_THREAD;
 }
+
+static inline bool irq_settings_set_chained(struct irq_desc *desc)
+{
+	return desc->status_use_accessors |= _IRQ_CHAINED;
+}
+
-- 
1.7.0.4