[PATCH v4 2/4] x86/irq: Fall back to irq_chip_retrigger_hierarchy() in fixup_irqs()

[Naman Jain <namjain@linux.microsoft.com>]

fixup_irqs() re-injects a pending interrupt on its new target CPU by
looking at the outermost domain chip and invoking its irq_retrigger()
callback directly. When the outermost chip does not implement
irq_retrigger(), the pending interrupt is silently dropped, which can
lead to lost interrupts on CPU hot-unplug.

Keep calling the outermost chip's irq_retrigger() when it is present,
but fall back to irq_chip_retrigger_hierarchy() otherwise, which walks
up the interrupt hierarchy until it finds a chip that implements
irq_retrigger().

While at it, use a scoped guard for desc->lock. VECTOR_RETRIGGERED is
now set only when the retrigger succeeds instead of unconditionally,
which is harmless today since apic_retrigger_irq() always returns 1.

Suggested-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
Reviewed-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
---
 arch/x86/kernel/irq.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 30122f0b3af96..e0163f7ac7368 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -470,6 +470,7 @@ void fixup_irqs(void)
 	struct irq_desc *desc;
 	struct irq_data *data;
 	struct irq_chip *chip;
+	int ret;
 
 	irq_migrate_all_off_this_cpu();
 
@@ -490,21 +491,23 @@ void fixup_irqs(void)
 	 * nothing else will touch it.
 	 */
 	for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) {
-		if (IS_ERR_OR_NULL(__this_cpu_read(vector_irq[vector])))
+		desc = __this_cpu_read(vector_irq[vector]);
+
+		if (IS_ERR_OR_NULL(desc))
 			continue;
 
 		if (is_vector_pending(vector)) {
-			desc = __this_cpu_read(vector_irq[vector]);
-
-			raw_spin_lock(&desc->lock);
+			guard(raw_spinlock)(&desc->lock);
 			data = irq_desc_get_irq_data(desc);
 			chip = irq_data_get_irq_chip(data);
-			if (chip->irq_retrigger) {
-				chip->irq_retrigger(data);
+			if (chip->irq_retrigger)
+				ret = chip->irq_retrigger(data);
+			else
+				ret = irq_chip_retrigger_hierarchy(data);
+			if (ret)
 				__this_cpu_write(vector_irq[vector], VECTOR_RETRIGGERED);
-			}
-			raw_spin_unlock(&desc->lock);
 		}
+
 		if (__this_cpu_read(vector_irq[vector]) != VECTOR_RETRIGGERED)
 			__this_cpu_write(vector_irq[vector], VECTOR_UNUSED);
 	}
-- 
2.43.0