[PATCH v3 1/1] x86/irq: handle chained interrupts during IRQ migration

[Sundar Iyer]

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.

Signed-off-by: Sundar Iyer <sundar.iyer@xxxxxxxxx>
Reviewed-by: Yang, Fei <fei.yang@xxxxxxxxx>
Tested-by: Ng, Cheon-woei <cheon-woei.ng@xxxxxxxxx>
---
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

 arch/x86/kernel/irq.c   |    6 ++++--
 include/linux/irq.h     |    1 +
 include/linux/irqdesc.h |    7 +++++++
 kernel/irq/chip.c       |    1 +
 kernel/irq/settings.h   |    7 +++++++
 5 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 6c0802e..ba7238b 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -249,8 +249,10 @@ 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)) {
+		/* 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 baa397e..7ec7826 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -87,6 +87,7 @@ enum {
 	IRQ_MOVE_PCNTXT		= (1 << 14),
 	IRQ_NESTED_THREAD	= (1 << 15),
 	IRQ_NOTHREAD		= (1 << 16),
+	IRQ_CHAINED		= (1 << 17),
 };
 
 #define IRQF_MODIFY_MASK	\
diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index 2d921b3..b170c69 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -120,6 +120,13 @@ 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 990965e..1c68de0 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -598,6 +598,7 @@ __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 f166783..1814115 100644
--- a/kernel/irq/settings.h
+++ b/kernel/irq/settings.h
@@ -14,6 +14,7 @@ enum {
 	_IRQ_NO_BALANCING	= IRQ_NO_BALANCING,
 	_IRQ_NESTED_THREAD	= IRQ_NESTED_THREAD,
 	_IRQF_MODIFY_MASK	= IRQF_MODIFY_MASK,
+	_IRQ_CHAINED		= IRQ_CHAINED,
 };
 
 #define IRQ_PER_CPU		GOT_YOU_MORON
@@ -26,6 +27,7 @@ enum {
 #define IRQ_NESTED_THREAD	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)
@@ -140,3 +142,8 @@ 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

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